U.S. patent application number 10/125719 was filed with the patent office on 2003-02-20 for viewing optical system and image pickup optical system and apparatus using the same.
Invention is credited to Amanai, Takahiro, Takeyama, Tetsuhide, Watanabe, Masachika.
Application Number | 20030034935 10/125719 |
Document ID | / |
Family ID | 18972486 |
Filed Date | 2003-02-20 |
United States Patent
Application |
20030034935 |
Kind Code |
A1 |
Amanai, Takahiro ; et
al. |
February 20, 2003 |
Viewing optical system and image pickup optical system and
apparatus using the same
Abstract
A viewing optical system for display apparatus allows
observation of a bright displayed image favorably corrected for
aberrations and is easy to assemble, resistant to impact such as
vibration, lightweight and compact. An ocular optical member for
leading an observation image formed by an observation image forming
member to an exit pupil has a first prism member and a second prism
member. The first prism member has a first entrance surface, a
reflecting surface and a first exit surface disposed to face each
other across a first prism medium. The second prism member has a
second entrance surface and a second exit surface disposed to face
each other across a second prism medium. The first and second prism
members are cemented together with a holographic element interposed
between the first exit surface and the second entrance surface. The
reflecting surface has a positive power. The first exit surface and
the second entrance surface are each formed from a plane or
cylindrical surface. The holographic element also has a plane of
cylindrical surface.
Inventors: |
Amanai, Takahiro;
(Sagamihara-shi, JP) ; Takeyama, Tetsuhide;
(Tokyo, JP) ; Watanabe, Masachika; (Tokyo,
JP) |
Correspondence
Address: |
KENYON & KENYON
1500 K STREET, N.W., SUITE 700
WASHINGTON
DC
20005
US
|
Family ID: |
18972486 |
Appl. No.: |
10/125719 |
Filed: |
April 19, 2002 |
Current U.S.
Class: |
345/7 ; 348/115;
359/13; 359/14; 359/362; 359/833; 396/384 |
Current CPC
Class: |
G02B 17/0816 20130101;
G02B 17/086 20130101; G02B 17/08 20130101 |
Class at
Publication: |
345/7 ; 359/14;
359/833; 396/384; 348/115; 359/13; 359/362 |
International
Class: |
G03H 001/00; G09G
005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2001 |
JP |
2001-122835 |
Claims
What we claim is:
1. A viewing optical system comprising: an observation image
forming member for forming an observation image to be viewed by an
observer; and an ocular optical member for leading the observation
image formed by said observation image forming member to an exit
pupil formed at a position of an observer's eyeball; said ocular
optical member including at least a first prism member and a second
prism member; said first prism member having at least: a first
entrance surface through which light rays from said observation
image enter said first prism member; a reflecting surface
reflecting the light rays within said first prism member; and a
first exit surface through which the light rays exit said first
prism member; wherein said first entrance surface, said reflecting
surface and said first exit surface are disposed to face each other
across a first prism medium; said second prism member having at
least: a second entrance surface through which the light rays
exiting from said first prism member enter said second prism
member; and a second exit surface through which the light rays exit
said second prism member; wherein said second entrance surface and
said second exit surface are disposed to face each other across a
second prism medium; said first prism member and said second prism
member being cemented together with a holographic element
interposed between said first exit surface and said second entrance
surface; wherein said reflecting surface of said first prism member
is a concave surface that gives a positive power to the light rays
when reflecting them; and wherein said first exit surface and said
second entrance surface are each formed from a plane surface or a
cylindrical surface.
2. A viewing optical system comprising: an observation image
forming member for forming an observation image to be viewed by an
observer; and an ocular optical member for leading the observation
image formed by said observation image forming member to an exit
pupil formed at a position of an observer's eyeball; said ocular
optical member including at least a first prism member and a second
prism member; said first prism member having at least: a first
entrance surface through which light rays from said observation
image enter said first prism member; a reflecting surface
reflecting the light rays within said first prism member; and a
first exit surface through which the light rays exit said first
prism member; wherein said first entrance surface, said reflecting
surface and said first exit surface are disposed to face each other
across a first prism medium; said second prism member having at
least: a second entrance surface through which the light rays
exiting from said first prism member enter said second prism
member; and a second exit surface through which the light rays exit
said second prism member; wherein said second entrance surface and
said second exit surface are disposed to face each other across a
second prism medium; said first prism member and said second prism
member being cemented together with a holographic element
interposed between said first exit surface and said second entrance
surface; wherein said reflecting surface of said first prism member
is a concave surface that gives a positive power to the light rays
when reflecting them; and wherein said first exit surface and said
second entrance surface are each formed from a spherical surface or
a toric surface satisfying the following
conditions:-2.0<Da/Ra<2.0 (2)-0.05<Db/Rb<0.05 (3)where
Ra and Da are a curvature radius and an outer diameter of the
surface in a direction of an axis where the surface has a larger
curvature, and Rb and Db are a curvature radius and an outer
diameter of the surface in a direction of an axis where the surface
has a smaller curvature.
3. A viewing optical system according to claim 1 or 2, wherein said
first entrance surface of said first prism member has a curved
surface configuration that gives a power to the light rays when
they pass through said surface, and said second exit surface of
said second prism member has a curved surface configuration that
gives a power to the light rays when they pass through said
surface.
4. A viewing optical system according to claim 1 or 2, wherein said
first prism medium and said second prism medium are a same
medium.
5. A viewing optical system according to claim 1 or 2, wherein the
first exit surface of said first prism member and the second
entrance surface of said second prism member have approximately a
same surface configuration.
6. A viewing optical system according to claim 1 or 2, wherein a
ghost light eliminating member that prevents ghost light from
entering the observer's eyeball is provided on a non-optical
functional surface other than optical functional surfaces of said
first prism member and said second prism member that transmit or
reflect the light rays.
7. A viewing optical system according to claim 1 or 2, wherein the
first entrance surface of said first prism member has a
rotationally asymmetric curved surface configuration.
8. A viewing optical system according to claim 7, wherein said
rotationally asymmetric curved surface configuration is a free-form
surface having only one plane of symmetry, and said plane of
symmetry is coincident with a plane (YZ-plane) in which an optical
axis is folded.
9. A viewing optical system according to claim 1 or 2, wherein said
holographic element is arranged to correct the light rays for both
rotationally symmetric and rotationally asymmetric components of
lateral chromatic aberration by reflection and diffraction.
10. A viewing optical system according to claim 1 or 2, wherein the
following condition (1) is
satisfied:45.degree.<.theta.<85.degree. (1)where .theta. is
an angle between a tangential plane at a position of intersection
between an axial principal ray and a substrate surface of said
holographic element and the axial principal ray traveling from a
surface of said viewing optical system closest to said exit pupil
to reach said exit pupil.
11. A viewing optical system according to claim 1 or 2, wherein
said second exit surface of said second prism member has a
rotationally asymmetric curved surface configuration that corrects
at least either one of rotationally asymmetric coma and astigmatism
produced in said ocular optical member.
12. A viewing optical system according to claim 11, wherein said
rotationally asymmetric curved surface configuration is a free-form
surface having only one plane of symmetry, and said plane of
symmetry is coincident with a plane (YZ-plane) in which an optical
axis is folded.
13. A viewing optical system according to claim 1 or 2, wherein
when a plane in which an optical axis is folded is a YZ-plane, and
a direction in which an axial principal ray travels from the exit
pupil to a surface of said viewing optical system closest to the
exit pupil is a Z-axis direction, and further a direction
perpendicularly intersecting the Z-axis direction and coincident
with a direction of decentration of the optical system is a Y-axis
direction, and further a direction of an axis that constitutes a
right-handed orthogonal coordinate system in combination with the
Y- and Z-axes is an X-axis direction, the following conditions are
satisfied:-1.0.ltoreq.Dx/Rx.ltoreq.0 (4)-1.0.ltoreq.Dy/Ry.ltoreq.0
(5)where Dx is a length in the X-axis direction of said observation
image forming member; Dy denotes a length in the Y-axis direction
of said observation image forming member; Rx denotes a curvature
radius in the X-axis direction of a substrate surface of said
holographic element; and Ry denotes a curvature radius in the
Y-axis direction of the substrate surface of said holographic
element.
14. A head-mounted image display apparatus comprising: a body unit
containing the viewing optical system according to claim 1 or 2; a
support member for supporting said body unit on a head of an
observer in such a manner that the exit pupil of said viewing
optical system is held at a position of an eyeball of the observer;
and a speaker member for giving voice to an ear of the
observer.
15. A head-mounted image display apparatus according to claim 14,
wherein said body unit has a viewing optical system for a right eye
and a viewing optical system for a left eye, and said speaker
member has a speaker member for a right ear and a speaker member
for a left ear.
16. A head-mounted image display apparatus according to claim 14,
wherein said speaker member is an earphone.
17. An image pickup optical system comprising: an image pickup
device placed in an image plane to pick up an image of an object;
an aperture stop placed in a pupil plane to reduce a brightness of
a light beam from the object; and an image-forming optical member
disposed between said image plane and said pupil plane to lead said
image of the object to said image plane; said image-forming optical
member including at least a second prism member and a first prism
member; said second prism member having at least: a third entrance
surface through which light rays emanating from the object and
passing through said aperture stop enter said second prism member;
and a third exit surface through which the light rays exit said
second prism member; wherein said third entrance surface and said
third exit surface are disposed to face each other across a second
prism medium; said first prism member having at least: a fourth
entrance surface through which the light rays exiting from said
second prism member enter said first prism member; a reflecting
surface reflecting the light rays within said first prism member;
and a fourth exit surface through which the light rays exit said
first prism member; wherein said fourth entrance surface, said
reflecting surface and said fourth exit surface are disposed to
face each other across a first prism medium; said second prism
member and said first prism member being cemented together with a
holographic element interposed between said third exit surface and
said fourth entrance surface; wherein said reflecting surface of
said first prism member is a concave surface that gives a positive
power to the light rays when reflecting them; and wherein said
third exit surface and said fourth entrance surface are each formed
from a plane surface or a cylindrical surface.
18. An image pickup optical system comprising: an image pickup
device placed in an image plane to pick up an image of an object;
an aperture stop placed in a pupil plane to reduce a brightness of
a light beam from the object; and an image-forming optical member
disposed between said image plane and said pupil plane to lead said
image of the object to said image plane; said image-forming optical
member including at least a second prism member and a first prism
member; said second prism member having at least: a third entrance
surface through which light rays emanating from the object and
passing through said aperture stop enter said second prism member;
and a third exit surface through which the light rays exit said
second prism member; wherein said third entrance surface and said
third exit surface are disposed to face each other across a second
prism medium; said first prism member having at least: a fourth
entrance surface through which the light rays exiting from said
second prism member enter said first prism member; a reflecting
surface reflecting the light rays within said first prism member;
and a fourth exit surface through which the light rays exit said
first prism member; wherein said fourth entrance surface, said
reflecting surface and said fourth exit surface are disposed to
face each other across a first prism medium; said second prism
member and said first prism member being cemented together with a
holographic element interposed between said third exit surface and
said fourth entrance surface; wherein said reflecting surface of
said first prism member is a concave surface that gives a positive
power to the light rays when reflecting them; and wherein said
third exit surface and said fourth entrance surface are each formed
from a spherical surface or a toric surface satisfying the
following conditions:-2.0<Da/Ra<2.0 (2)-0.05<Db/Rb<0.05
(3)where Ra and Da are a curvature radius and an outer diameter of
the surface in a direction of an axis where the surface has a
larger curvature, and Rb and Db are a curvature radius and an outer
diameter of the surface in a direction of an axis where the surface
has a smaller curvature.
19. An image pickup optical system according to claim 17 or 18,
wherein said fourth exit surface of said first prism member has a
curved surface configuration that gives a power to the light rays
when they pass through said surface, and said third entrance
surface of said second prism member has a curved surface
configuration that gives a power to the light rays when they pass
through said surface.
20. An image pickup optical system according to claim 17 or 18,
wherein said first prism medium and said second prism medium are a
same medium.
21. An image pickup optical system according to any one of claims
17 or 20, wherein the fourth entrance surface of said first prism
member and the third exit surface of said second prism member have
approximately a same surface configuration.
22. An image pickup optical system according to claim 17 or 18,
wherein a ghost light eliminating member that prevents ghost light
from entering the image pickup device is provided on a non-optical
functional surface other than optical functional surfaces of said
first prism member and said second prism member that transmit or
reflect the light rays.
23. An image pickup optical system according to claim 17 or 18,
wherein the fourth exit surface of said first prism member has a
rotationally asymmetric curved surface configuration.
24. An image pickup optical system according to claim 23, wherein
said rotationally asymmetric curved surface configuration is a
free-form surface having only one plane of symmetry, and said plane
of symmetry is coincident with a plane (YZ-plane) in which an
optical axis is folded.
25. An image pickup optical system according to claim 17 or 18,
wherein said holographic element is arranged to correct the light
rays for both rotationally symmetric and rotationally asymmetric
components of lateral chromatic aberration by reflection and
diffraction.
26. An image pickup optical system according to claim 17 or 18,
wherein the following condition (1) is
satisfied:45.degree.<.theta.<85.degr- ee. (1)where .theta. is
an angle between a tangential plane at a position of intersection
between an axial principal ray and a substrate surface of said
holographic element and the axial principal ray traveling from said
stop to reach a surface of said image pickup optical system closest
to said stop.
27. An image pickup optical system according to claim 17 or 18,
wherein said third entrance surface of said second prism member has
a rotationally asymmetric curved surface configuration that
corrects at least either one of rotationally asymmetric coma and
astigmatism produced in said image-forming optical member.
28. An image pickup optical system according to claim 27, wherein
said rotationally asymmetric curved surface configuration is a
free-form surface having only one plane of symmetry, and said plane
of symmetry is coincident with a plane (YZ-plane) in which an
optical axis is folded.
29. An image pickup optical system according to claim 17 or 18,
wherein when a plane in which an optical axis is folded is a
YZ-plane, and a direction in which an axial principal ray travels
from said stop to a surface of said image pickup optical system
closest to said stop is a Z-axis direction, and further a direction
perpendicularly intersecting the Z-axis direction and coincident
with a direction of decentration of the optical system is a Y-axis
direction, and further a direction of an axis that constitutes a
right-handed orthogonal coordinate system in combination with the
Y- and Z-axes is an X-axis direction, the following conditions are
satisfied:-1.0.ltoreq.Dx/Rx.ltoreq.0 (4)-1.0.ltoreq.Dy/Ry.ltoreq.0
(5)where Dx is a length in the X-axis direction of said image
pickup device; Dy denotes a length in the Y-axis direction of said
image pickup device; Rx denotes a curvature radius in the X-axis
direction of a substrate surface of said holographic element; and
Ry denotes a curvature radius in the Y-axis direction of the
substrate surface of said holographic element.
Description
[0001] This application claims benefit of Japanese Patent
Application No. 2001-122835 filed in Japan on Apr. 20, 2001, the
contents of which are incorporated by this reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a viewing optical system
and an image pickup optical system and also pertains to an
apparatus using the viewing optical system and/or the image pickup
optical system. More particularly, the present invention relates to
an optical system for use in an image display apparatus or the like
that can be retained on an observer's head or face and can also be
added to a portable telephone or a portable information
terminal.
[0003] In recent years, image display apparatus, particularly head-
or face-mounted image display apparatus, have been developed
actively for the purpose of enabling the user to enjoy viewing
wide-screen images personally. Meanwhile, portable telephones have
recently become widespread, and there have been increasing demands
that portable information terminals should display images and
character data on a large screen.
[0004] Under these circumstances, Japanese Patent Application
Unexamined Publication Numbers [hereinafter referred to as "JP(A)"]
Hei 7-140414 and Hei 9-171151 propose an optical system using a
half-mirror as an oblique mirror for branching an optical path in a
prism optical system including a concave mirror having a small
amount of decentration.
[0005] U.S. Pat. No. 5,093,567 and JP(A) 2000-241751 and
2000-180787 propose an optical system in which a first prism having
a triangular configuration and a convex lens action is disposed on
the eye side of the optical system, and a second prism is disposed
to face the first prism across a small air space. These
conventional techniques propose a viewing optical system that folds
an optical path without loss of light quantity by making use of a
total reflection phenomenon occurring owing to the refractive index
difference between glass and air produced by the presence of the
small air space between the two prisms.
[0006] U.S. Pat. No. 4,874,214 proposes a viewing optical system
using a holographic element. In this viewing optical system,
holographic elements are used at two places, i.e. on an oblique
mirror surface that is a plane surface, and on a spherical
substrate surface.
[0007] In the above-mentioned JP(A) Hei 7-140414 and Hei 9-171151,
an oblique mirror disposed in a prism optical system is formed from
a half-mirror. With this arrangement, light emitted from an image
display device passes through the half-mirror twice. Therefore, the
amount of light reduces to 1/4, and thus the displayed image
becomes unfavorably dark. In order to prevent this problem, it is
necessary to illuminate the image display device by using bright
illumination or the like consuming more electric power. In a case
where the luminance of the light source cannot be increased owing
to power consumption or the capability of the light source device,
it becomes impossible to view the displayed image under the bright
sun.
[0008] In the viewing optical systems proposed in U.S. Pat. No.
5,093,567 and JP(A) 2000-241751 and 2000-180787, it is necessary to
adjust the optical axes of the two prisms with respect to each
other because a small air space is provided between the prisms.
Therefore, the assembly cost increases. Further, it is likely that
the optical axes of the two prisms will be displaced from each
other when an impact or vibration is applied to an apparatus
including the viewing optical system.
[0009] The optical system proposed in U.S. Pat. No. 5,093,567 is a
relay optical system and hence large in size and heavy in weight.
Therefore, it is difficult to use the optical system in a portable
telephone or a portable information terminal.
[0010] The viewing optical system proposed in U.S. Pat. No.
4,874,214 has a spherical holographic element on a spherical
surface. Incidentally, a holographic element has two different
kinds of optical power, i.e. an optical power derived from a
geometrical configuration, and an optical power based on the
diffractive effect of the holographic element. Two different kinds
of power obtained when a holographic element is provided on a
substrate member having a spherical surface, for example, will be
explained below with reference to FIGS. 29(a) and 29(b). As shown
in FIG. 29(a), the holographic element has a power based on the
difference in density of interference fringes, e.g. the pitch of
periodic structures in the holographic element. In addition, the
holographic element has an optical power derived from the
geometrical configuration thereof, as shown in FIG. 29(b).
Regarding the optical power based on the geometrical configuration,
the optical powers .PHI. of a conventional optical refractive lens
and conventional reflecting mirrors can be calculated according to
the following equations:
1 Refracting system: .PHI. = (n-1) (1/R) Surface-coated mirror:
.PHI. = 2/R Back-coated mirror: .PHI. = 2n/R where .PHI.: the
optical power based on the geometrical configuration n: the
refractive index of the medium R: the radius of curvature of the
hologram substrate
[0011] Accordingly, it will be understood from a comparison of the
surface-coated mirror with the back-coated mirror that the
back-coated mirror can obtain a given optical power based on the
geometrical configuration with a gentler curvature (larger
curvature radius R) by 1/n than in the case of the surface-coated
mirror.
[0012] That is, even if the geometrical configuration of a
reflection type holographic element is formed with a gentle
curvature (large curvature radius R), it is possible to obtain a
large optical power based on the geometrical configuration by
filling the inside of the holographic element with a medium having
a refractive index n, e.g. a glass or plastic material, as in the
case of the back-coated mirror.
[0013] Thus, aberrations occurring at the hologram surface can be
suppressed by employing an arrangement that allows a large optical
power to be produced with a gentle curvature (large curvature
radius R) in the optical system.
[0014] However, in the viewing optical system stated in the
above-mentioned U.S. Pat. No. 4,874,214, the space between the
plane surface and the spherical surface is not filled with a glass
or plastic medium. Therefore, it is necessary to form the
geometrical configuration with a reduced curvature radius R in
order to ensure the required optical power derived from the
geometrical configuration having a spherical shape.
[0015] When the geometrical configuration is formed with a reduced
curvature radius R, aberrations occurring at this reflecting
surface increase, and it becomes difficult to effect favorable
image display. Further, because there is no optical surface in the
optical path between the image plane and the above-described plane
surface, it is difficult to correct distortion favorably.
[0016] Further, the hologram surface in U.S. Pat. No. 4,874,214 is
a spherical surface. In general, methods of bonding a hologram are
divided into one type in which a film-shaped hologram is bonded to
a substrate surface, and another type in which a substrate surface
is sprayed with a liquid photopolymer or the like as a hologram
recording material. The latter method needs to carry out exposure
and development after the spraying process. Considering
mass-productivity, it is preferable to adopt the method wherein a
film-shaped holographic element is bonded to a substrate because
this method allows exposure and development to be performed before
the holographic element is bonded to the substrate.
[0017] However, film-shaped holograms supplied from manufacturers
are, in general, plane holograms. It is not easy to bond a
film-type holographic element on a three-dimensional curved surface
uniformly.
SUMMARY OF THE INVENTION
[0018] The present invention was made to solve the above-described
problems with the prior art.
[0019] An object of the present invention is to provide a viewing
optical system for image display apparatus that allows observation
of a bright displayed image favorably corrected for aberrations and
is easy to assemble, resistant to impact such as vibration,
lightweight and compact, and also provide an image pickup optical
system and an apparatus using the viewing optical system and/or the
image pickup optical system.
[0020] To attain the above-described object, the present invention
provides a viewing optical system having an observation image
forming member for forming an observation image to be viewed by an
observer and an ocular optical member for leading the observation
image formed by the observation image forming member to an exit
pupil formed at the position of an observer's eyeball.
[0021] The ocular optical member includes at least a first prism
member and a second prism member.
[0022] The first prism member has, at least, a first entrance
surface through which light rays from the observation image enter
the first prism member, a reflecting surface reflecting the light
rays within the first prism member, and a first exit surface
through which the light rays exit the first prism member. The first
entrance surface, the reflecting surface and the first exit surface
are disposed to face each other across a first prism medium.
[0023] The second prism member has, at least, a second entrance
surface through which the light rays exiting from the first prism
member enter the second prism member, and a second exit surface
through which the light rays exit the second prism member. The
second entrance surface and the second exit surface are disposed to
face each other across a second prism medium.
[0024] The first prism member and the second prism member are
cemented together with a holographic element interposed between the
first exit surface and the second entrance surface.
[0025] The reflecting surface of the first prism member is a
concave surface that gives a positive power to the light rays when
reflecting them.
[0026] The first exit surface and the second entrance surface are
each formed from a plane surface or a cylindrical surface.
Alternatively, the first exit surface and the second entrance
surface are each formed from a spherical surface or a toric surface
satisfying the following conditions:
-2.0<Da/Ra<2.0 (2)
-0.05<Db/Rb<0.05 (3)
[0027] where Ra and Da are a curvature radius and an outer diameter
of the surface in the direction of an axis where the surface has a
larger curvature, and Rb and Db are a curvature radius and an outer
diameter of the surface in the direction of an axis where the
surface has a smaller curvature.
[0028] In addition, the present invention provides an image pickup
optical system having an image pickup device placed in an image
plane to pick up an image of an object, an aperture stop placed in
a pupil plane to reduce the brightness of a light beam from the
object, and an image-forming optical member disposed between the
image plane and the pupil plane to lead the object image to the
image plane.
[0029] The image-forming optical member includes at least a second
prism member and a first prism member.
[0030] The second prism member has, at least, a third entrance
surface through which light rays emanating from the object and
passing through the aperture stop enter the second prism member,
and a third exit surface through which the light rays exit the
second prism member. The third entrance surface and the third exit
surface are disposed to face each other across a second prism
medium.
[0031] The first prism member has, at least, a fourth entrance
surface through which the light rays exiting from the second prism
member enter the first prism member, a reflecting surface
reflecting the light rays within the first prism member, and a
fourth exit surface through which the light rays exit the first
prism member. The fourth entrance surface, the reflecting surface
and the fourth exit surface are disposed to face each other across
a first prism medium.
[0032] The second prism member and the first prism member are
cemented together with a holographic element interposed between the
third exit surface and the fourth entrance surface.
[0033] The reflecting surface of the first prism member is a
concave surface that gives a positive power to the light rays when
reflecting them.
[0034] The third exit surface and the fourth entrance surface are
each formed from a plane surface or a cylindrical surface.
Alternatively, the third exit surface and the fourth entrance
surface are each formed from a spherical surface or a toric surface
satisfying the following conditions:
-2.0<Da/Ra<2.0 (2)
-0.05<Db/Rb<0.05 (3)
[0035] where Ra and Da are a curvature radius and an outer diameter
of the surface in the direction of an axis where the surface has a
larger curvature, and Rb and Db are a curvature radius and an outer
diameter of the surface in the direction of an axis where the
surface has a smaller curvature.
[0036] The reasons for adopting the above-described arrangements in
the present invention, together with the functions thereof, will be
described below.
[0037] First, the viewing optical system will be described.
[0038] The viewing optical system according to the present
invention has an observation image forming member for forming an
observation image to be viewed by an observer and an ocular optical
member for leading the observation image formed by the observation
image forming member to an exit pupil formed at the position of an
observer's eyeball. The ocular optical member includes at least a
first prism member and a second prism member. The first prism
member has, at least, a first entrance surface through which light
rays from the observation image enter the first prism member, a
reflecting surface reflecting the light rays within the first prism
member, and a first exit surface through which the light rays exit
the first prism member. The first entrance surface, the reflecting
surface and the first exit surface are disposed to face each other
across a first prism medium. The second prism member has, at least,
a second entrance surface through which the light rays exiting from
the first prism member enter the second prism member, and a second
exit surface through which the light rays exit the second prism
member. The second entrance surface and the second exit surface are
disposed to face each other across a second prism medium.
[0039] Thus, the inside of the ocular optical member is filled with
a medium, e.g. a glass or plastic material, thereby increasing the
optical power based on the surface configuration of each optical
functional surface, and thus favorably correcting aberrations, e.g.
spherical aberration and comatic aberration.
[0040] Further, in the above-described viewing optical system
according to the present invention, the first prism member and the
second prism member are cemented together with a holographic
element interposed between the first exit surface and the second
entrance surface.
[0041] If a holographic element is used as an oblique mirror for
branching an optical path, a diffraction efficiency close to 100%
can be obtained when light rays are reflected and diffracted. Thus,
it becomes possible to display a bright image without loss of light
quantity. If the two prism members, i.e. the prism member closer to
the image display device (observation image forming member), and
the eye-side prism member, are cemented together into a single
member with a holographic element interposed therebetween, it is
possible to solve such problems as optical axis displacement that
may occur during assembly owing to the presence of an air space,
and troublesomeness in setting. Thus, it is possible to attain a
viewing optical system easy to assemble and resistant to impact
such as vibration.
[0042] Further, if the holographic element is cemented between the
first prism member and the second prism member, it is possible to
keep the holographic element out of dust and hence possible to
prevent dust or other foreign matter from being undesirably
observed as an enlarged image without the need to provide a
dustproof member separately. It is also possible to prevent water
from entering the holographic element from the outside, which would
otherwise swell the holographic element, causing a change in the
peak wavelength of the diffraction efficiency.
[0043] Further, in the above-described viewing optical system
according to the present invention, the reflecting surface of the
first prism member is a concave surface that gives a positive power
to the light rays when reflecting them.
[0044] Further, the viewing optical system according to the present
invention does not form an intermediate image between the image
display device and the observer's eye. That is, the viewing optical
system has no relay optical system. Therefore, it is constructed in
the form of a lightweight and compact viewing optical system.
[0045] Further, it is desirable in the viewing optical system
according to the present invention that the first entrance surface
of the first prism member should have a curved surface
configuration that gives a power to light rays when they pass
through the surface, and the second exit surface of the second
prism member should have a curved surface configuration that gives
a power to light rays when they pass through the surface.
[0046] Further, it is preferable in the viewing optical system
according to the present invention that the first prism medium and
the second prism medium should be the same kind of medium.
[0047] Further, it is preferable in the viewing optical system
according to the present invention that the first exit surface of
the first prism member and the second entrance surface of the
second prism member should have approximately the same surface
configuration.
[0048] It should be noted that the term "approximately the same
surface configuration" as used herein means that a difference in
surface configuration within the range of manufacturing errors is
permitted.
[0049] Further, it is preferable in the viewing optical system
according to the present invention that a ghost light eliminating
member that prevents ghost light from entering the observer's
eyeball should be provided on a non-optical functional surface
other than the optical functional surfaces of the first and second
prism members that transmit or reflect light rays.
[0050] The ghost light eliminating member is particularly effective
when provided on the bottom and side surfaces of the ocular optical
member when the first entrance surface of the first prism member is
defined as the top surface. The term "non-optical functional
surfaces" includes the region outside the ray effective diameter of
the first entrance surface, the region outside the ray effective
diameter of the reflecting surface of the first prism member, and
the region outside the ray effective diameter of the second exit
surface of the second prism member. Providing a ghost light
eliminating member on each of these regions is also effective.
[0051] Further, it is preferable in the viewing optical system
according to the present invention that the first entrance surface
of the first prism member should have a rotationally asymmetric
curved surface configuration.
[0052] If a transmitting surface (i.e. the first entrance surface
of the first prism member) is disposed in front of an image forming
member, e.g. an image display device, as in the present invention,
distortion can be corrected favorably. It should be noted that the
surface in front of the image forming member may be a rotationally
symmetric surface. However, it is even more desirable to use a
free-form surface from the viewpoint of correcting decentration
aberrations occurring when optical functional surfaces are
decentered for the purpose of minimizing the size of the viewing
optical system.
[0053] Further, it is preferable in the viewing optical system
according to the present invention that the rotationally asymmetric
curved surface configuration of the first entrance surface of the
first prism member should be a free-form surface having only one
plane of symmetry, and the plane of symmetry of the free-form
surface should be coincident with a plane (YZ-plane) in which the
optical axis is folded.
[0054] Further, it is preferable in the viewing optical system
according to the present invention that the holographic element
should be arranged to correct light rays for both rotationally
symmetric and rotationally asymmetric components of lateral
chromatic aberration by reflection and diffraction.
[0055] If the rotationally symmetric and rotationally asymmetric
components of lateral chromatic aberration are corrected by a
reflection type holographic element, a high contrast can be
realized.
[0056] In the viewing optical system according to the present
invention, the holographic element cemented between the first and
second prism members is a reflection type hologram. If the tilt
angle of the surface of the holographic element is set at an angle
different from 45 degrees with respect to the visual axis (i.e. the
axial principal ray reaching the exit pupil from the surface of the
viewing optical system closest to the exit pupil), the overall
thickness of the viewing optical system can be reduced, and thus a
compact and lightweight optical system can be realized. To correct
decentration aberrations occurring owing to the arrangement in
which an oblique mirror comprising the holographic element is set
at an angle different from 45 degrees with respect to the visual
axis, free-form surfaces are used as a surface through which light
from the image display device enters the prism, a surface
reflecting diffracted light from the reflection type holographic
element, and a surface in front of the observer's eye. Further, a
power is given to the substrate surface configuration of the
reflection type holographic element. Thus, coma and field curvature
are corrected favorably.
[0057] That is, it is important to satisfy the following
condition:
45.degree.<.theta.<85.degree. (1)
[0058] where .theta. is, as shown in FIG. 24, the angle between a
tangential plane at a position A of intersection between the axial
principal ray 2 and the substrate surface of the holographic
element 6 and the axial principal ray 2 reaching the exit pupil 1
from the surface 4.sub.1 of the viewing optical system closest to
the exit pupil 1.
[0059] If the angle .theta. is not larger than the lower limit of
the condition (1), i.e. 45.degree., the tilt of the oblique mirror
comprising the holographic element becomes excessively small.
Consequently, the viewing optical system increases in thickness,
resulting in a large and heavyweight optical system. If the angle
.theta. is not smaller than the upper limit, i.e. 85.degree., the
amount of decentration of the viewing optical system becomes
excessively large. Consequently, it is difficult to correct
decentration aberrations. Thus, it becomes difficult to observe an
image having a high contrast and favorably corrected for
distortion.
[0060] It is more desirable to satisfy the following condition:
55.degree.<.theta.<80.degree. (1-1)
[0061] The meaning of the lower and upper limits of the condition
(1-1) is the same as that of the lower and upper limits of the
condition (1).
[0062] It is even more desirable to satisfy the following
condition:
65.degree.<.theta.<75.degree. (1-2)
[0063] The meaning of the lower and upper limits of the condition
(1-2) is the same as that of the lower and upper limits of the
condition (1).
[0064] In the viewing optical system according to the present
invention, the inside of the viewing optical system is filled with
a medium, e.g. a glass or plastic material, in the form of the
first and second prism members, thereby increasing the optical
power based on the surface configuration of each optical functional
surface, and thus favorably correcting aberrations, e.g. coma and
field curvature.
[0065] Incidentally, the reflection type holographic element
provided as an oblique mirror in the present invention is, in
general, a film-type planar holographic element. It is desirable
that the first exit surface of the first prism member and the
second entrance surface of the second prism member, each of which
serves as a substrate to which the planar holographic element is
bonded, should have a plane surface configuration or a cylindrical
surface configuration.
[0066] It is also possible to use a spherical surface or a toric
surface as a substrate to which the planar holographic element is
bonded. If the spherical or toric surface satisfies the following
conditions, mass-production can be realized by using the planar
holographic element:
-2.0<Da/Ra<2.0 (2)
-0.05<Db/Rb<0.05 (3)
[0067] where Ra and Da are a curvature radius and an outer diameter
of the surface in the direction of an axis where the surface has a
larger curvature, and Rb and Db are a curvature radius and an outer
diameter of the surface in the direction of an axis where the
surface has a smaller curvature.
[0068] In the conditions (2) and (3), the lower limits, i.e. -2.0
and -0.05, are limit values in a case where the holographic element
is bonded to a concave surface. The upper limits, i.e. 2.0 and
0.05, are limit values in a case where the holographic element is
bonded to a convex surface. If Da/Ra and Db/Rb are not within the
ranges defined by the conditions (2) and (3), the planar
holographic element wrinkles at the peripheral portion of the
curved surface. Thus, it becomes difficult to bond the holographic
element uniformly and hence impossible to obtain the desired
optical performance of the holographic element.
[0069] It is more desirable to satisfy the following
conditions:
-2.0<Da/Ra<2.0 (2-1)
-0.02<Db/Rb<0.02 (3-1)
[0070] The meaning of the lower and upper limits of the conditions
(2-1) and (3-1) is the same as that of the lower and upper limits
of the conditions (2) and (3).
[0071] It is even more desirable to satisfy the following
conditions:
-2.0<Da/Ra<2.0 (2-2)
-0.015<Db/Rb<0.015 (3-2)
[0072] The meaning of the lower and upper limits of the conditions
(2-2) and (3-2) is the same as that of the lower and upper limits
of the conditions (2) and (3).
[0073] It is preferable in the viewing optical system according to
the present invention that the second exit surface of the second
prism member should have a rotationally asymmetric curved surface
configuration that corrects at least either one of rotationally
asymmetric coma and astigmatism produced in the ocular optical
member.
[0074] Further, it is preferable in the viewing optical system
according to the present invention that the rotationally asymmetric
curved surface configuration of the second exit surface of the
second prism member should be a free-form surface having only one
plane of symmetry, and the plane of symmetry of the free-form
surface should be coincident with a plane (YZ-plane) in which the
optical axis is folded.
[0075] It is desirable in the present invention that the surfaces
constituting the first prism member and those constituting the
second prism member should be rotationally asymmetric surfaces,
e.g. free-form surfaces, from the viewpoint of realizing an optical
system capable of favorably correcting rotationally asymmetric
distortion and exhibiting favorable telecentricity. However, those
surfaces may be formed from rotationally symmetric surfaces, e.g.
spherical surfaces, aspherical surfaces, or anamorphic
surfaces.
[0076] In the viewing optical system according to the present
invention, a light beam from an observation image formed by the
observation image forming member is passed through the first
entrance surface to enter the first prism member. The light beam
entering the first prism member is made incident on a volume
hologram at a first incident angle within the range of angle
selectivity of the hologram. After being reflected and diffracted
from the hologram, the light beam is reflected by the reflecting
surface. The reflected light beam is incident on the volume
hologram surface again at a second incident angle. At this time,
because the second incident angle is not within the range of angle
selectivity of the volume hologram, the diffraction efficiency is
extremely low. Consequently, the incident light beam passes through
the first exit surface substantially as it is, and enters the
second prism member through the second entrance surface.
[0077] The light beam entering the second prism member exits the
second prism member through the second exit surface as it is, and
is then led to the observer's eyeball.
[0078] In the viewing optical system according to the present
invention, an optical member, e.g. a prism, a plane-parallel plate
of glass, or a positive or negative lens, may be disposed between
the first entrance surface of the first prism member and the
observation image forming member.
[0079] Further, in the viewing optical system according to the
present invention, an optical member, e.g. a prism, a
plane-parallel plate of glass, or a positive or negative lens, may
be disposed between the second exit surface of the second prism
member and the exit pupil.
[0080] In the case of using an image display device, e.g. an LCD
(Liquid Crystal Display), it is necessary in order to perform image
display with high contrast to enlarge and display an image through
an optical system with favorable telecentricity. The described
arrangements of the optical system according to the present
invention are applicable not only to a viewing optical system but
also to an image pickup optical system. In the latter case, when an
image pickup device, e.g. a CCD, is used, it is also important to
pick up an image through an optical system with favorable
telecentricity from the viewpoint of preventing shading or the
like.
[0081] In the present invention, the eye relief is long relative to
the focal length of the entire optical system. Therefore, the
extra-axial principal rays are tilted with respect to the image
display device in a direction in which the extra-axial light beams
converge. To realize an optical system having enhanced
telecentricity and an increased eye relief as well as a compact
structure, it is desirable to place a negative power in the optical
path near the image display device (image pickup device) and a
positive power on the eye (object) side.
[0082] The above means that the optical system has an arrangement
obtained by inverting a retrofocus type optical system. That is, it
is important to give a negative power to an oblique mirror surface
in the optical system near the image display device. To ensure
telecentricity over the whole area of an image field with a
difference in length between two orthogonal axis directions, it is
particularly important that the oblique mirror surface should have
a larger negative power in an axis direction of the aspect ratio in
which the oblique mirror surface is longer than in the direction of
the other axis.
[0083] Let us assume that the length in the X-axis direction of the
image display device is Dx, and the length in the Y-axis direction
of the image display device is Dy. That is, the aspect ratio of the
image display device is denoted by Dx:Dy. Further, the curvature
radius in the X-axis direction of the oblique mirror surface is
assumed to be Rx, and the curvature radius in the Y-axis direction
of the oblique mirror surface is assumed to be Ry. On these
assumptions, if the following conditions are satisfied,
telecentricity can be ensured to obtain favorable optical
performance in a case where there is no displacement in the X-axis
direction (this is true of all Examples described later):
-1.0.ltoreq.Dx/Rx.ltoreq.0 (4)
-1.0.ltoreq.Dy/Ry.ltoreq.0 (5)
[0084] If the upper limits of the conditions (4) and (5), i.e. 0,
are exceeded, the oblique mirror surface has a positive power.
Consequently, the principal rays further tilt in the direction of
convergence, and it becomes impossible to capture a high-contrast
image from the image display device. If Dx/Rx and Dy/Ry are smaller
than the lower limits of the conditions (4) and (5), i.e. -1.0, the
image display device is excessively large in size, or the negative
power of the oblique mirror surface is excessively large.
Consequently, the tilt angle of the principal rays becomes rather
divergent. Accordingly, it becomes impossible to capture a
high-contrast image from the image display device.
[0085] It is more desirable to satisfy the following
conditions:
-0.5.ltoreq.Dx/Rx.ltoreq.0 (4-1)
-0.5.ltoreq.Dy/Ry.ltoreq.0 (5-1)
[0086] The meaning of the lower and upper limits of the conditions
(4-1) and (5-1) is the same as that of the lower and upper limits
of the conditions (4) and (5).
[0087] It is even more desirable to satisfy the following
conditions:
-0.1.ltoreq.Dx/Rx.ltoreq.0 (4-2)
-0.1.ltoreq.Dy/Ry.ltoreq.0 (5-2)
[0088] The meaning of the lower and upper limits of the conditions
(4-2) and (5-2) is the same as that of the lower and upper limits
of the conditions (4) and (5).
[0089] With the above-described arrangement, a holographic element
is provided on an oblique mirror surface having a plane or
cylindrical substrate surface configuration. Alternatively, a
planar holographic element is provided on an oblique mirror surface
having a spherical or toric substrate surface configuration
satisfying the conditions (2) and (3) for preventing the planar
holographic element from wrinkling at the peripheral portion
thereof when bonded to the spherical or toric surface. This
arrangement dispenses with the need to provide a half-mirror for
branching the optical path or to provide an air space. Accordingly,
it is possible to obtain a viewing optical system that allows
observation of a bright displayed image favorably corrected for
aberrations with minimal loss of light quantity and is easy to
assemble, resistant to impact such as vibration, lightweight and
compact and further permits a hologram to be bonded easily, and it
is also possible to obtain an apparatus using the viewing optical
system.
[0090] It should be noted that the described arrangements of the
optical system according to the present invention are applicable
not only to a viewing system but also to an image pickup
system.
[0091] The image pickup optical system according to the present
invention has an image pickup device placed in an image plane to
pick up an image of an object, an aperture stop placed in a pupil
plane to reduce the brightness of a light beam from the object, and
an image-forming optical member disposed between the image plane
and the pupil plane to lead the object image to the image plane.
The image-forming optical member includes at least a second prism
member and a first prism member. The second prism member has, at
least, a third entrance surface through which light rays emanating
from the object and passing through the aperture stop enter the
second prism member, and a third exit surface through which the
light rays exit the second prism member. The third entrance surface
and the third exit surface are disposed to face each other across a
second prism medium. The first prism member has, at least, a fourth
entrance surface through which the light rays exiting from the
second prism member enter the first prism member, a reflecting
surface reflecting the light rays within the first prism member,
and a fourth exit surface through which the light rays exit the
first prism member. The fourth entrance surface, the reflecting
surface and the fourth exit surface are disposed to face each other
across a first prism medium. The second prism member and the first
prism member are cemented together with a holographic element
interposed between the third exit surface and the fourth entrance
surface. The reflecting surface of the first prism member is a
concave surface that gives a positive power to the light rays when
reflecting them.
[0092] The third exit surface and the fourth entrance surface are
each formed from a plane surface or a cylindrical surface.
[0093] Alternatively, the third exit surface and the fourth
entrance surface are each formed from a spherical surface or a
toric surface satisfying the following conditions:
-2.0<Da/Ra<2.0 (2)
-0.05<Db/Rb<0.05 (3)
[0094] where Ra and Da are a curvature radius and an outer diameter
of the surface in the direction of an axis where the surface has a
larger curvature, and Rb and Db are a curvature radius and an outer
diameter of the surface in the direction of an axis where the
surface has a smaller curvature.
[0095] That is, the image pickup optical system according to the
present invention is formed by replacing the observation image
forming member, the exit pupil and the ocular optical member in the
viewing optical system according to the present invention with the
image pickup device, the aperture stop and the image-forming
optical member, respectively.
[0096] It is also preferable in the image pickup optical system to
adopt arrangements similar to those of the viewing optical system,
e.g. the above-described conditional expressions.
[0097] Further, in the viewing optical system according to the
present invention, the reflecting surface of the first prism member
should preferably be formed by mirror coating.
[0098] The reflecting surface of the first prism member may be
arranged in the form of a totally reflecting surface that reflects
a light beam incident thereon at an angle exceeding the total
reflection critical angle but transmits a light beam incident
thereon at an angle not exceeding the total reflection critical
angle. It is also possible to provide a light-transmitting optical
member on the reflecting surface side of the first prism
member.
[0099] With this arrangement, see-through observation can be
performed. Accordingly, the user can continue wearing a head- or
face-mounted image display apparatus using the viewing optical
system according to the present invention without interference with
the normal observation of the outside. Thus, it is possible to save
time and effort to put on or take off the head- or face-mounted
image display apparatus.
[0100] It is also possible to view both an external observation
image and an image from the image display device as a superimposed
multiple image.
[0101] It should be noted that the reflecting surface of the first
prism member may be formed from a half-mirror to allow see-through
observation.
[0102] It is also possible to construct a head-mounted image
display apparatus having a body unit containing an image display
device and any of the foregoing viewing optical systems according
to the present invention arranged as an ocular optical system. The
head-mounted image display apparatus further has a support member
for supporting the body unit on the head of an observer in such a
manner that the exit pupil of the viewing optical system is held at
the position of an eyeball of the observer, and a speaker member
for giving voice to an ear of the observer.
[0103] The above-described head-mounted image display apparatus may
be arranged such that the body unit has a viewing optical system
for a right eye and a viewing optical system for a left eye, and
the speaker member has a speaker member for a right ear and a
speaker member for a left ear.
[0104] In the head-mounted image display apparatus, the speaker
member may be an earphone.
[0105] In the viewing optical system according to the present
invention, a light ray from the object center that passes through
the center of the pupil and reaches the center of the image plane
in backward ray tracing is defined as an axial principal ray. In
the image pickup optical system according to the present invention,
a light rays from the object center that passes through the center
of the aperture stop and reaches the center of the image plane in
forward ray tracing is defined as an axial principal ray. In the
optical system according to the present invention, if at least one
reflecting surface is not decentered with respect to the axial
principal ray, the axial principal ray travels along the same
optical path when incident on and reflected from the reflecting
surface, and thus the axial principal ray is intercepted in the
optical system undesirably. As a result, an image is formed from
only a light beam whose central portion is shaded. Consequently,
the center of the image is unfavorably dark, or no image is formed
in the center of the image field. For this reason, a decentered
prism is used as each prism member in the present invention.
[0106] When a reflecting surface with a power is decentered with
respect to the axial principal ray, it is desirable that at least
one of the surfaces constituting each prism member used in the
present invention should be a rotationally asymmetric surface. It
is particularly preferable from the viewpoint of correcting
aberrations that at least one reflecting surface of the prism
members should be a rotationally asymmetric surface.
[0107] To use an optical path in a common region repeatedly by
folding the optical path, the optical system has to be decentered.
However, if the optical system is formed into a decentered optical
system in order to fold the optical path, decentration aberrations
such as rotationally asymmetric distortion and rotationally
asymmetric field curvature occur. To correct the decentration
aberrations, a rotationally asymmetric surface is used as stated
above.
[0108] The rotationally asymmetric surface used in the present
invention can be formed from an anamorphic surface, a toric
surface, or a plane-symmetry free-form surface having only one
plane of symmetry. It is preferable to use a free-form surface
having only one plane of symmetry as a rotationally asymmetric
surface.
[0109] In the present invention, the axial principal ray is defined
as follows. In the viewing optical system, a light ray passing
through the center of the exit pupil and reaching the center of the
observation image forming member in the backward ray tracing is
defined as an axial principal ray. In the image pickup optical
system, a light ray passing through the center of the aperture stop
and reaching the center of the image pickup device in the forward
ray tracing is defined as an axial principal ray. An optical axis
defined by a straight line along which the axial principal ray
travels from the center of the exit pupil or the aperture stop
until it intersects the second exit surface of the second prism
member is defined as a Z-axis. An axis perpendicularly intersecting
the Z-axis in the decentration plane of each surface constituting
the second prism member is defined as a Y-axis. An axis
perpendicularly intersecting the Z-axis and also perpendicularly
intersecting the Y-axis is defined as an X-axis. Further, the
center of the exit pupil or the aperture stop is defined as the
origin of the coordinate system in the viewing optical system or
the image pickup optical system according to the present invention.
Further, in the present invention, the surface Nos. are put in the
order of backward ray tracing from the exit pupil toward the
observation image forming member or in the order of forward ray
tracing from the aperture stop toward the image pickup device, as
stated above. The direction along which the axial principal ray
from the exit pupil reaches the observation image forming member or
the direction along which the axial principal ray from the aperture
stop reaches the image pickup device is defined as a positive
direction of the Z-axis. The direction in which the Y-axis extends
toward the observation image forming member or the direction in
which the Y-axis extends toward the image pickup device is defined
as a positive direction of the Y-axis. The direction in which the
X-axis constitutes a right-handed system in combination with the Y-
and Z-axes is defined as a positive direction of the X-axis.
[0110] Free-form surfaces used in the present invention are defined
by the following equation (a). The Z-axis of the defining equation
is the axis of a free-form surface. 1 Z = cr 2 / [ 1 + { 1 - ( 1 +
k ) c 2 r 2 } ] + j = 2 .infin. C j X m Y n ( a )
[0111] In Eq. (a), the first term is a spherical surface term, and
the second term is a free-form surface term.
[0112] In the spherical surface term:
[0113] c: the curvature at the vertex
[0114] k: a conic constant
[0115] r={square root}{square root over ( )}(X.sup.2+Y.sup.2)
[0116] The free-form surface term is given by 2 j = 2 .infin. C j X
m Y n = C 2 X + C 3 Y + C 4 X 2 + C 5 XY + C 6 Y 2 + C 7 X 3 + C 8
X 2 Y + C 9 XY 2 + C 10 Y 3 + C 11 X 4 + C 12 X 3 Y + C 13 X 2 Y 2
+ C 14 XY 3 + C 15 Y 4 + C 16 X 5 + C 17 X 4 Y + C 18 X 3 Y 2 + C
19 X 2 Y 3 + C 20 XY 4 + C 21 Y 5 + C 22 X 6 + C 23 X 5 Y + C 24 X
4 Y 2 + C 25 X 3 Y 3 + C 26 X 2 Y 4 + C 27 XY 5 + C 28 Y 6 + C 29 X
7 + C 30 X 6 Y + C 31 X 5 Y 2 + C 32 X 4 Y 3 + C 33 X 3 Y 4 + C 34
X 2 Y 5 + C 35 XY 6 + C 36 Y 7
[0117] where C.sub.j (j is an integer of 2 or higher) are
coefficients, and j={(m+n).sup.2+m+3n}/2+1 (m and n are integers of
zero or higher).
[0118] In general, the above-described free-form surface does not
have planes of symmetry in both the XZ- and YZ-planes. However, a
free-form surface having only one plane of symmetry parallel to the
YZ-plane is obtained by making all terms of odd-numbered degrees
with respect to X zero. For example, in the above defining equation
(a), the coefficients of the terms C.sub.2, C.sub.5, C.sub.7,
C.sub.9, C.sub.12, C.sub.14, C.sub.16, C.sub.18, C.sub.20,
C.sub.23, C.sub.25, C.sub.27, C.sub.29, C.sub.31, C.sub.33,
C.sub.35, . . . are set equal to zero. By doing so, it is possible
to obtain a free-form surface having only one plane of symmetry
parallel to the YZ-plane.
[0119] A free-form surface having only one plane of symmetry
parallel to the XZ-plane is obtained by making all terms of
odd-numbered degrees with respect to Y zero. For example, in the
above defining equation (a), the coefficients of the terms C.sub.3,
C.sub.5, C.sub.8, C.sub.10, C.sub.12, C.sub.14, C.sub.17, C.sub.19,
C.sub.21, C.sub.23, C.sub.25, C.sub.27, C.sub.30, C.sub.32,
C.sub.34, C.sub.36, . . . are set equal to zero. By doing so, it is
possible to obtain a free-form surface having only one plane of
symmetry parallel to the XZ-plane.
[0120] Furthermore, the direction of decentration is determined in
correspondence to either of the directions of the above-described
planes of symmetry. For example, with respect to the plane of
symmetry parallel to the YZ-plane, the direction of decentration of
the optical system is determined to be the Y-axis direction. With
respect to the plane of symmetry parallel to the XZ-plane, the
direction of decentration of the optical system is determined to be
the X-axis direction. By doing so, rotationally asymmetric
aberrations due to decentration can be corrected effectively, and
at the same time, productivity can be improved.
[0121] It should be noted that the above defining equation (a) is
shown as merely an example, and that the feature of the present
invention resides in that rotationally asymmetric aberrations due
to decentration are corrected and, at the same time, productivity
is improved by using a rotationally asymmetric surface having only
one plane of symmetry. Therefore, the same advantageous effect can
be obtained for any defining equation other than the above defining
equation (a) that expresses such a rotationally asymmetric
surface.
[0122] In the present invention, the reflecting surface provided in
the prism member may be a plane-symmetry free-form surface having
only one plane of symmetry.
[0123] The configuration of an anamorphic surface is defined by the
following equation (b). A straight line passing through the origin
of the surface configuration perpendicularly to the optical surface
is the axis of the anamorphic surface.
Z=(Cx.multidot.X.sup.2+Cy.multidot.Y.sup.2)/[1+{1-(1+Kx)Cx.sup.2.multidot.-
X.sup.2-(1+Ky)Cy.sup.2.multidot.Y.sup.2}.sup.1/2]+.SIGMA.Rn{(1-Pn)X.sup.2+-
(1+Pn)Y.sup.2}.sup.(n+1) (b)
[0124] Assuming that n=4 (polynomial of degree 4), for example, an
anamorphic surface may be expressed by an expanded form of the
above equation (b) as follows: 3 Z = ( Cx X 2 + Cy Y 2 ) / [ 1 + {
1 - ( 1 + Kx ) Cx 2 X 2 - ( 1 + Ky ) Cy 2 Y 2 } 1 / 2 ] + R 1 { ( 1
- P 1 ) X 2 + ( 1 + P 1 ) Y 2 } 2 + R 2 { ( 1 - P 2 ) X 2 + ( 1 + P
2 ) Y 2 } 3 + R 3 { ( 1 - P 3 ) X 2 + ( 1 + P 3 ) Y 2 } 4 + R 4 { (
1 - P 4 ) X 2 + ( 1 + P 4 ) Y 2 } 5 ( c )
[0125] where Z is the amount of deviation from a plane tangent to
the origin of the surface configuration; Cx is the curvature in the
X-axis direction; Cy is the curvature in the Y-axis direction; Kx
is the conic coefficient in the X-axis direction; Ky is the conic
coefficient in the Y-axis direction; Rn is the rotationally
symmetric component of the spherical surface term; and Pn is the
rotationally asymmetric component of the aspherical surface term.
It should be noted that the radius of curvature Rx in the X-axis
direction and the radius of curvature Ry in the Y-axis direction
are related to the curvatures Cx and Cy as follows:
Rx=1/Cx, Ry=1/Cy
[0126] Toric surfaces include an X-toric surface and a Y-toric
surface, which are defined by the following equations (d) and (e),
respectively. A straight line passing through the origin of the
surface configuration perpendicularly to the optical surface is the
axis of the toric surface. The X-toric surface is given by
[0127]
F(X)=Cx.multidot.X.sup.2/[1+{1-(1+K)Cx.sup.2.multidot.X.sup.2}.sup.-
1/2]+AX.sup.4+BX.sup.6+CX.sup.8+DX.sup.10
Z=F(X)+(1/2)Cy{Y.sup.2+Z.sup.2-F(X).sup.2} (d)
[0128] The Y-toric surface is given by
F(Y)=Cy.multidot.Y.sup.2/[1+{1-(1+K)Cy.sup.2.multidot.Y.sup.2}.sup.1/2]+AY-
.sup.4+BY.sup.6+CY.sup.8+DY.sup.10
Z=F(Y)+(1/2)Cx{X.sup.2+Z.sup.2-F(Y).sup.2} (e)
[0129] In the above equations, Z is the amount of deviation from a
plane tangent to the origin of the surface configuration; Cx is the
curvature in the X-axis direction; Cy is the curvature in the
Y-axis direction; K is a conic coefficient; and A, B, C and D are
aspherical coefficients, respectively. It should be noted that the
radius of curvature Rx in the X-axis direction and the radius of
curvature Ry in the Y-axis direction are related to the curvatures
Cx and Cy as follows:
Rx=1/Cx, Ry=1/Cy
[0130] Holographic elements include two different types, i.e.
relief holograms, and volume holograms. Relief holograms have the
nature that the incident angle selectivity and wavelength
selectivity are low, and they diffract light of specific wavelength
incident thereon at a specific angle to form an image by the
desired order of light. However, the relief holograms also diffract
light of other wavelengths incident thereon at other angles as
unwanted orders of light to form an undesired image. On the other
hand, the volume holograms have the nature that the incident angle
selectivity and wavelength selectivity are high, and hence they
diffract only light of specific wavelength incident thereon at a
specific angle to form an image by the desired order of light. The
volume holograms transmit substantially all the other orders of
light as zero-order light and are therefore unlikely to form an
undesired image by unwanted orders of light.
[0131] Therefore, if a reflection type volume hologram is used as a
holographic element in the present invention, it is possible to
prevent image blur due to unwanted orders of diffracted light and
hence possible to obtain a clear observation image.
[0132] It should be noted that a volume hologram (HOE) used as a
holographic element in the present invention is defined as follows.
FIG. 25 is a principle diagram for defining the HOE in the present
invention.
[0133] First, tracing of rays of wavelength .lambda. incident on
and exiting from the HOE surface is given by the following equation
(f) using the optical path difference function .PHI..sub.0 on the
HOE surface defined with respect to the reference wavelength
.lambda..sub.0=HWL:
n.sub.dQ.sub.d.times.N=n.sub.iQ.sub.i.times.N+m
(.lambda./.lambda..sub.0) .gradient..PHI..sub.0.times.N (f)
[0134] where N is the normal vector to the HOE surface; n.sub.i
(n.sub.d) is the refractive index on the incidence side (exit
side); and Q.sub.i (Q.sub.d) is the incidence (exit) vector (unit
vector). In addition, m=HOR is the order of diffraction of emergent
light.
[0135] Assuming that the HOE is produced (defined) by two point
sources of reference wavelength .lambda..sub.0, that is, as shown
in FIG. 25, by interference between object light from a light
source at point P.sub.1=(HX1, HY1, HZ1) and reference light from a
light source at point P.sub.2=(HX2, HY2, HZ2),
.PHI..sub.0=.PHI..sub.0.sup.2P=n.sub.2.multidot.s.sub.2.multidot.r.sub.2-n-
.sub.1.multidot.s.sub.1.multidot.r.sub.1
[0136] where r.sub.1 (r.sub.2) is the distance (>0) from the
point P.sub.1 (point P.sub.2) to a predetermined coordinate point P
on the HOE surface; n.sub.1 (n.sub.2) is the refractive index of a
medium in which the HOE is placed during the production
(definition) on the side where the point P.sub.1 (point P.sub.2) is
located; and s.sub.1=HV1 and S.sub.2=HV2 are signs to consider the
direction of travel of light. The sign is REA=+1 when the light
source is a divergent light source (real point source). Conversely,
when the light source is a convergent light source (virtual point
source), the sign is VIR=-1. Regarding the definition of the HOE in
lens data, the refractive index n.sub.1 (n.sub.2) of a medium in
which the HOE is placed during the production (definition) is the
refractive index of a medium with which the HOE surface is in
contact on the side where the point P.sub.1 (P.sub.2) is present in
the lens data.
[0137] In a general case, reference light and object light used to
produce an HOE are not always spherical wave. The optical path
difference function .PHI..sub.0 of the HOE in this case may be
expressed by adding a polynomially-expressed additive phase term
.PHI..sub.0.sup.Poly (optical path difference function at the
reference wavelength .lambda..sub.0) as follows:
.PHI..sub.0=.PHI..sub.0.sup.2P+.PHI..sub.0.sup.Poly (g)
[0138] In the above equation (g), the polynomial expression is as
follows: 4 0 Poly = j H j x m y n = H 1 x + H 2 y + H 3 x 2 + H 4
xy + H 5 y 2 + H 6 x 3 + H 7 x 2 y + H 8 xy 2 + H 9 y 3 +
[0139] In general, it may be defined as follows:
j={(m+n).sup.2+m+3n}/2
[0140] In the above expression, H.sub.3 is the coefficient of each
term.
[0141] For the convenience of optical design, the optical path
difference function .PHI..sub.0 may be expressed by only the
additive term to define the HOE as follows:
.PHI..sub.0=.PHI..sub.0.sup.Poly
[0142] For example, if the two point sources P.sub.1 (P.sub.2) are
made coincident with each other, the interference component
.PHI..sub.0.sup.2P of the optical path difference function
.PHI..sub.0 is zero. This is equivalent to expressing the optical
path difference function substantially only by the additive term
(polynomial expression).
[0143] It should be noted that the foregoing description of the HOE
has been made all with regard to local coordinates based on the HOE
origin.
[0144] Examples of constituent parameters defining an HOE are as
follows:
2 Surface No. Radius of curvature Surface separation Object plane
.infin. .infin. 1 .infin. (stop) 100 2 150 (HOE {circle over (1)})
-75 HOE {circle over (1)} HV1 (s.sub.1): REA (+1) HV2 (s.sub.2):
VIR (-1) NOR (m): 1 HX1 = 0 HY1 = -3.40 .times. 10.sup.9 HZ1 =
-3.40 .times. 10.sup.9 HX2 = 0 HY2 = 2.50 .times. 10 HZ2 = -7.04
.times. 10 HWL (.lambda..sub.0) = 544 H1 -1.39 .times. 10.sup.-21
H2 -8.57 .times. 10.sup.-5 H3 -1.50 .times. 10.sup.-4
[0145] The following is a description of the principle of
reflection, diffraction and transmission at the surface of a volume
hologram used in the present invention. Regarding the simulation of
diffraction efficiency, let us show the simulation of diffraction
efficiency for s-polarized light component based on Kogelnik's
theory. The simulation was performed on Example 1 (described
later). However, this is true of the other examples.
[0146] In this example, LED light sources having center wavelengths
of 630 nm, 520 nm and 470 nm, respectively, were used as light
sources for R, G and B bands, together with narrow-band filters to
narrow the bandwidth to about .+-.5 nm to 10 nm in center
wavelength. Let us show the results of calculation of the
diffraction efficiency at a volume hologram surface for the axial
principal ray in the G band, by way of example. It should be noted
that the calculation results were obtained under the conditions
that the reference refractive index was 1.5, the refractive index
modulation was 0.05, and the thickness of the holographic element
was 10 .mu.m. The diffraction efficiency when the angle of
incidence of the axial principal ray on the volume hologram surface
was 47.3.degree. and the reflection diffraction angle was
46.9.degree. is shown in FIGS. 26 and 27. FIG. 26 is a graph
showing the diffraction efficiency (ordinate axis) with respect to
the incident angle (abscissa axis) of the axial principal ray of
wavelength 520 nm. FIG. 27 is a graph showing the diffraction
efficiency (ordinate axis) for the axial principal ray incident at
an angle of 47.3.degree. with respect to wavelength (abscissa
axis).
[0147] It will be understood from FIG. 26 that a high diffraction
efficiency, i.e. approximately 100%, can be obtained at an incident
angle in the neighborhood of 47.3.degree.. From FIG. 27, it will be
understood that a favorable reflection and diffraction efficiency
can be obtained in a wavelength range of 520 nm.+-.20 nm.
Meanwhile, light rays reflected from the reflecting surface of the
first prism member after being reflected and diffracted from the
volume hologram surface are incident on the hologram surface again.
At this time, the axial principal ray is incident on the hologram
surface at an angle of 18.7.degree.. It will be understood from
FIG. 26 that the incident angle of 18.7.degree. is not within the
angle selectivity range of the volume holographic element, in which
it exhibits a high diffraction efficiency, and the diffraction
efficiency is as low as about 0%. Therefore, the light rays pass
through the volume holographic element as they are.
[0148] The above discussion is true of the R band and the B band.
It is also possible to use a switching holographic element
employing a liquid crystal as the above-described holographic
element.
[0149] Still other objects and advantages of the invention will in
part be obvious and will in part be apparent from the
specification.
[0150] The invention accordingly comprises the features of
construction, combinations of elements, and arrangement of parts
which will be exemplified in the construction hereinafter set
forth, and the scope of the invention will be indicated in the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0151] FIG. 1 is a sectional view of an optical system according to
Example 1 of the present invention, taken along a YZ-plane
containing an optical axis thereof.
[0152] FIG. 2 is a sectional view of an optical system according to
Example 2 of the present invention, taken along a YZ-plane
containing an optical axis thereof.
[0153] FIG. 3 is a sectional view of an optical system according to
Example 3 of the present invention, taken along a YZ-plane
containing an optical axis thereof.
[0154] FIG. 4 is a sectional view of an optical system according to
Example 4 of the present invention, taken along a YZ-plane
containing an optical axis thereof.
[0155] FIG. 5 is a sectional view of an optical system according to
Example 5 of the present invention, taken along a YZ-plane
containing an optical axis thereof.
[0156] FIG. 6 is an aberrational diagram showing image distortion
in Example 1.
[0157] FIG. 7 is an aberrational diagram showing lateral
aberrations for the R band (red band) in Example 1.
[0158] FIG. 8 is an aberrational diagram showing lateral
aberrations for the G band (green band) in Example 1.
[0159] FIG. 9 is an aberrational diagram showing lateral
aberrations for the B band (blue band) in Example 1.
[0160] FIG. 10 is a sectional view of a viewing optical system
provided with a ghost light eliminating member, taken along a
YZ-plane containing an optical axis thereof.
[0161] FIG. 11 is a diagram illustrating how light passing through
a holographic element without being diffracted gives an adverse
effect as ghost light.
[0162] FIG. 12 is a diagram showing a head-mounted image display
apparatus for both eyes using a viewing optical system according to
the present invention in a state where it is fitted on an
observer's head.
[0163] FIG. 13 is a sectional view of the head-mounted image
display apparatus shown in FIG. 12.
[0164] FIG. 14 is a diagram showing a head-mounted image display
apparatus for a single eye using a viewing optical system according
to the present invention in a state where it is fitted on an
observer's head.
[0165] FIG. 15 is a perspective view showing the external
appearance of an electronic camera to which an image pickup optical
system and a viewing optical system according to the present
invention are applied, as viewed from the front side thereof.
[0166] FIG. 16 is a perspective view of the electronic camera shown
in FIG. 15, as viewed from the rear side thereof.
[0167] FIG. 17 is a sectional view showing an arrangement of the
electronic camera in FIG. 15.
[0168] FIG. 18 is a conceptual view of another electronic camera to
which an image pickup optical system and a viewing optical system
according to the present invention are applied.
[0169] FIGS. 19(a) and 19(b) are conceptual views of a video
endoscope system to which an image pickup optical system and a
viewing optical system according to the present invention are
applied.
[0170] FIG. 20 is a perspective view showing a personal computer
incorporating an image pickup optical system according to the
present invention as an objective optical system, as viewed from
the front side thereof, in a state where a cover is open.
[0171] FIG. 21 is a sectional view of a photographic optical system
of the personal computer shown in FIG. 20.
[0172] FIG. 22 is a side view of the personal computer in the state
shown in FIG. 20.
[0173] FIG. 23(a) is a front view of a portable telephone
incorporating an image pickup optical system according to the
present invention as an objective optical system.
[0174] FIG. 23(b) is a side view of the portable telephone shown in
FIG. 23(a).
[0175] FIG. 23(c) is a sectional view of a photographic optical
system of the portable telephone shown in FIG. 23(a).
[0176] FIG. 24 is a diagram for describing the definition of angle
74 .
[0177] FIG. 25 is a principle diagram for defining an HOE in the
present invention.
[0178] FIG. 26 is a graph showing the diffraction efficiency of a
volume hologram according to the present invention with respect to
the incident angle of an axial principal ray of wavelength 520
nm.
[0179] FIG. 27 is a graph showing the diffraction efficiency of a
volume hologram according to the present invention for an axial
principal ray incident at an angle of 47.3.degree. with respect to
wavelength.
[0180] FIG. 28 is a diagram showing a desirable arrangement for an
optical system according to the present invention when an HOE is
disposed in a prism constituting the optical system.
[0181] FIGS. 29(a) and 29(b) are a front view and a side view,
respectively, for describing two different kinds of power obtained
when a holographic element is provided on a substrate member having
a spherical surface.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0182] Examples of the viewing optical system and image pickup
optical system according to the present invention will be described
below.
[0183] It should be noted that constituent parameters of Examples 1
to 5 will be shown later. In each example, as shown in FIG. 1 by
way of example, an axial principal ray 2 is defined by a light ray
from the center of an exit pupil 1 (or an aperture stop 14; the
rolling center of an observer's eyeball) that passes through a
second prism member 4 and a first prism member 3 to reach the
center of an LCD 5 (or an image pickup device 13) provided as an
observation image forming member. An optical axis defined by a
straight line along which the axial principal ray 2 travels until
it intersects the exit pupil-side surface 4 of the second prism
member 4 is defined as a Z-axis. An axis perpendicularly
intersecting the Z-axis in the decentration plane of each surface
constituting the prism is defined as a Y-axis. An axis
perpendicularly intersecting the optical axis (Z-axis) and also
perpendicularly intersecting the Y-axis is defined as an X-axis.
Further, the center of the exit pupil 1 (or the aperture stop 14)
is defined as the origin of the coordinate system. Further, the
direction along which the axial principal ray 2 from the exit pupil
1 (or the aperture stop 14) travels to reach the LCD 5 (or the
image pickup device 13) is defined as a positive direction of the
Z-axis. The direction in which the Y-axis extends toward the LCD 5
(or the image pickup device 13) is defined as a positive direction
of the Y-axis. The direction in which the X-axis constitutes a
right-handed system in combination with the Y- and Z-axes is
defined as a positive direction of the X-axis.
[0184] In Examples 1 to 5, the first prism member 3 and the second
prism member 4 are decentered in the YZ-plane, and one and only
plane of symmetry of each rotationally asymmetric free-form surface
provided in the first and second prism members 3 and 4 is the
YZ-plane.
[0185] Regarding decentered surfaces, each surface is given
displacements in the X-, Y- and Z-axis directions (X, Y and Z,
respectively) of the vertex position of the surface from the origin
of the optical system, and tilt angles (degrees) of the center axis
of the surface [the Z-axis of the above equation (a) in regard to
free-form surfaces; the Z-axis of the above equation (d) or (e) in
the case of toric surfaces] with respect to the X-, Y- and Z-axes
(.alpha., .beta. and .gamma., respectively). In this case, positive
.alpha. and .beta. mean counterclockwise rotation relative to the
positive directions of the corresponding axes, and positive .gamma.
means clockwise rotation relative to the positive direction of the
Z-axis. It should be noted that the way of rotating the center axis
of each surface through .alpha., .beta. and .gamma. is as follows.
First, the center axis of the surface and the XYZ orthogonal
coordinate system are rotated through .alpha. counterclockwise
about the X-axis. Then, the rotated center axis of the surface is
rotated through .beta. counterclockwise about the Y-axis of the new
coordinate system, and the coordinate system once rotated is also
rotated through .beta. counterclockwise about the Y-axis. Then, the
center axis of the surface, which has been rotated twice, is
rotated through .gamma. clockwise about the Z-axis of the new
coordinate system.
[0186] Among optical functional surfaces constituting the optical
system in each of Examples 1 to 5, a specific surface and a surface
subsequent thereto are given a surface separation when these
surfaces form a coaxial optical system. In addition, the radius of
curvature of each spherical surface and the refractive index and
Abbe's number of each medium are given according to the
conventional method.
[0187] The configuration of each free-form surface used in the
present invention is defined by the above equation (a). The Z-axis
of the defining equation is the axis of the free-form surface.
[0188] Free-form surfaces may also be defined by Zernike
polynomials. That is, the configuration of a free-form surface may
be defined by the following equation (h). The Z-axis of the
defining equation (h) is the axis of Zernike polynomial. A
rotationally asymmetric surface is defined by polar coordinates of
the height of the Z-axis with respect to the XY-plane. In the
equation (h), R is the distance from the Z-axis in the XY-plane,
and A is the azimuth angle about the Z-axis, which is expressed by
the angle of rotation measured from the X-axis. 5 x = R .times. cos
( A ) y = R .times. sin ( A ) Z = D 2 + D 3 R cos ( A ) + D 4 R sin
( A ) + D 5 R 2 cos ( 2 A ) + D 6 ( R 2 - 1 ) + D 7 R 2 sin ( 2 A )
+ D 8 R 3 cos ( 3 A ) + D 9 ( 3 R 3 - 2 R ) cos ( A ) + D 10 ( 3 R
3 - 2 R ) sin ( A ) + D 11 R 3 sin ( 3 A ) + D 12 R 4 cos ( 4 A ) +
D 13 ( 4 R 4 - 3 R 2 ) cos ( 2 A ) + D 14 ( 6 R 4 - 6 R 2 + 1 ) + D
15 ( 4 R 4 - 3 R 2 ) sin ( 2 A ) + D 16 R 4 sin ( 4 A ) + D 17 R 5
cos ( 5 A ) + D 18 ( 5 R 5 - 4 R 3 ) cos ( 3 A ) + D 19 ( 10 R 5 -
12 R 3 + 3 R ) cos ( A ) + D 20 ( 10 R 5 - 12 R 3 + 3 R ) sin ( A )
+ D 21 ( 5 R 5 - 4 R 3 ) sin ( 3 A ) + D 22 R 5 sin ( 5 A ) + D 23
R 6 cos ( 6 A ) + D 24 ( 6 R 6 - 5 R 4 ) cos ( 4 A ) + D 25 ( 15 R
6 - 20 R 4 + 6 R 2 ) cos ( 2 A ) + D 26 ( 20 R 6 - 30 R 4 + 12 R 2
- 1 ) + D 27 ( 15 R 6 - 20 R 4 + 6 R 2 ) sin ( 2 A ) + D 28 ( 6 R 6
- 5 R 4 ) sin ( 4 A ) + D 29 R 6 sin ( 6 A ) ( h )
[0189] where D.sub.m (m is an integer of 2 or higher) are
coefficients. It should be noted that to design an optical system
symmetric with respect to the X-axis direction, D.sub.4, D.sub.5,
D.sub.6, D.sub.10, D.sub.11, D.sub.12, D.sub.13, D.sub.14,
D.sub.20, D.sub.21, D.sub.22 should be used.
[0190] The configuration of a rotationally asymmetric free-form
surface can also be defined by the following equation (i). The
Z-axis of the defining equation (i) is the axis of the rotationally
asymmetric surface.
z.times..SIGMA..sub.n.SIGMA..sub.mC.sub.nmx.sup.ny.sup.n-m (i)
[0191] where .SIGMA..sub.n indicates that n of .SIGMA. is from 0 to
k, and .SIGMA..sub.m indicates that m of .SIGMA. is from 0 to
n.
[0192] Although in Examples 1 to 5 of the present invention the
surface configuration is expressed by a free-form surface using the
above equation (a), it should be noted that the same advantageous
effect can be obtained by using the above equation (h) or (i).
[0193] Examples 1 to 5 will be described below specifically. In
these examples, the present invention will be described as an image
display apparatus using a viewing optical system.
[0194] FIGS. 1 to 5 are sectional views of viewing optical systems
according to Examples 1 to 5 of the present invention, taken along
the YZ-plane containing the optical axis. The viewing optical
systems of these examples each have an LCD 5 disposed on the image
plane side of the optical system as an image forming member for
displaying an image to be viewed by an observer and an ocular
optical member for leading the observation image formed by the
image forming member to an exit pupil 1 formed at the position of
an observer's eyeball (pupil plane) to observe the image.
[0195] The ocular optical member includes a first prism member 3
and a second prism member 4.
[0196] In the description of each example, the surface Nos. of the
optical system are put in the order of tracing (backward ray
tracing) from the exit pupil 1 toward the LCD 5, as a general rule,
and the surfaces of the first and second prism members 3 and 4 are
also shown by ordinal numbers in the backward ray tracing. Further,
a light beam traveling along an optical path connecting the exit
pupil 1 and the LCD 5 through the optical system is referred to as
"the first light beam".
[0197] The first prism member 3 has a first entrance surface
3.sub.3, a reflecting surface 3.sub.2, and a first exit surface
3.sub.1, which are disposed to face each other across a transparent
prism medium, e.g. a glass or plastic material.
[0198] The second prism member 4 has a second entrance surface
4.sub.2 and a second exit surface 4.sub.1, which are disposed to
face each other across a transparent prism medium, e.g. a glass or
plastic material.
[0199] The first prism member 3 and the second prism member 4 are
cemented together with a reflection type volume hologram (HOE) 6
interposed therebetween as a holographic element.
[0200] It should be noted that the prism medium of the first prism
member 3 and the prism medium of the second prism member 4 are the
same medium, i.e. the same glass material or the same plastic
material.
[0201] In all Examples 1 to 5, the first entrance surface 3.sub.3
of the first prism member 3 is disposed on the side of the first
prism member 3 closer to the LCD 5 to transmit light rays from the
observation image so that the light rays enter the first prism
member 3. The first entrance surface 3.sub.3 is a free-form surface
having only one plane of symmetry that gives a power to light rays
when they pass through the surface.
[0202] The reflecting surface 3.sub.2 reflects light rays within
the first prism member 3. In all Examples 1 to 5, the reflecting
surface 3.sub.2 is a concave surface (a free-form surface in the
examples) that gives a positive power to the light rays when
reflecting them. The reflecting surface 3.sub.2 is provided with
mirror coating.
[0203] The first exit surface 3.sub.1 is a surface through which
light rays exit the first prism member 3. In Example 1, the first
exit surface 3.sub.1 is a cylindrical surface having a curvature in
the X-axis direction but no curvature in the Y-axis direction. In
Example 2, the first exit surface 3.sub.1 is a cylindrical surface
having a curvature in the Y-axis direction but no curvature in the
X-axis direction. In Example 3, the first exit surface 3.sub.1 is a
plane surface. In Example 4, the first exit surface 3.sub.1 is a
toric surface having different curvatures in the X- and Y-axis
directions. In Example 5, the first exit surface 3.sub.1 is a
spherical surface.
[0204] The second entrance surface 4.sub.2 of the second prism
member 4 is disposed on the side of the second prism member 4
closer to the first prism member 3 to transmit the light rays
exiting from the first prism member 3 so that the light rays enter
the second prism member 4. In all Examples 1 to 5, the second
entrance surface 4.sub.2 has approximately the same surface
configuration as that of the first exit surface 3.sub.1 of the
first prism member 3.
[0205] The second exit surface 4.sub.1 is a surface through which
the light rays exit the second prism member 4. In all Examples 1 to
5, the second exit surface 4.sub.1 is a free-form surface having
only one plane of symmetry that gives a power to light rays when
they pass through the surface. The second exit surface 4.sub.1
corrects at least either one of rotationally asymmetric coma and
astigmatism produced in the ocular optical member.
[0206] It should be noted that the one and only plane of symmetry
of the free-form surfaces constituting the first entrance surface
3.sub.3 and the reflecting surface 3.sub.2 of the first prism
member 3 and the second exit surface 4.sub.1 of the second prism
member 4 is coincident with a plane (YZ-plane) in which the optical
axis is folded (see FIGS. 1 to 5).
[0207] As has been stated above, the volume hologram 6 is arranged
so that when the first light beam is incident thereon at a first
incident angle (e.g. 47.3.degree. for light rays of wavelength 520
nm in Example 1), the volume hologram 6 diffracts and reflects the
incident light beam, whereas when the first light beam is incident
thereon at an angle other than the first incident angle, the volume
hologram 6 transmits the incident light beam.
[0208] In the viewing optical systems in Examples 1 to 5, the first
light beam emitted from the LCD 5 enters the first prism member 3
through the first entrance surface 3.sub.3. Thereafter, the first
light beam is incident at the first incident angle on the volume
hologram 6 bonded to the first exit surface 3.sub.1. At this time,
the first light beam is diffracted and reflected toward the
reflecting surface 3.sub.2 by the volume hologram 6 at a reflection
diffraction efficiency close to 100%. The first light beam is
reflected by the reflecting surface 3.sub.2 and incident at an
angle other than the first incident angle on the volume hologram 6
bonded to the first exit surface 3.sub.1. The incident angle at
this time is not within the diffraction efficiency angle
selectivity range of the volume hologram 6, in which it exhibits a
high diffraction efficiency. Therefore, the incident first light
beam passes through the volume hologram 6 and thus exits the first
prism member 3. Thereafter, the first light beam enters the second
prism member 4 through the second entrance surface 4.sub.2 of the
second prism member 4 and passes through the second exit surface
4.sub.1 to exit the second prism member 4. Then, the first light
beam is led to the exit pupil 1.
[0209] Although the present invention is described as a viewing
optical system in Examples 1 to 5, it should be noted that the
present invention can be constructed in the form of an image pickup
optical system by disposing an image pickup device 13 in the image
plane of the viewing optical system in place of the LCD 5 and
placing an aperture stop 14 in the pupil plane (i.e. at the
position of the exit pupil 1) to reduce the brightness of a light
beam from the object.
[0210] In that case, the first entrance surface 3.sub.3 of the
first prism member 3 acts as a surface (fourth exit surface)
through which light rays exit the first prism member 3. The first
exit surface 3.sub.1 of the first prism member 3 acts as a surface
(fourth entrance surface) through which light rays exiting from the
second prism member 4 enter the first prism member 3. The second
entrance surface 4.sub.2 of the second prism member 4 acts as a
surface (third exit surface) through which light rays exit the
second prism member 4. The second exit surface 4.sub.1 of the
second prism member 4 acts as a surface (third entrance surface)
through which light rays emanating from the object and passing
through the aperture stop 14 enter the second prism member 4.
[0211] In a case where the present invention is constructed in the
form of an image pickup optical system, light rays emanating from
the object and passing through the aperture stop 14 enter the
second prism member 4 through the third entrance surface 4.sub.1.
Thereafter, the light rays are incident at an angle other than the
first incident angle on the volume hologram 6 bonded to the third
exit surface 4.sub.2 of the second prism member 4. The incident
angle at this time is not within the diffraction efficiency angle
selectivity range of the volume hologram 6, in which it exhibits a
high diffraction efficiency. Therefore, the incident first light
beam passes through the volume hologram 6 and thus exits the second
prism member 4. Then, the first light beam enters the first prism
member 3 through the fourth entrance surface 3.sub.1 of the first
prism member 3. Thereafter, the first light beam is reflected by
the reflecting surface 3.sub.2 of the first prism member 3 and
incident at an angle approximately equal to the first incident
angle (e.g. 47.3.degree. for light rays of wavelength 520 nm in
Example 1) on the volume hologram 6 bonded to the fourth entrance
surface 3.sub.1. The incident first light beam is diffracted and
reflected by the volume hologram 6 at a reflection and diffraction
efficiency close to 100% and passes through the fourth exit surface
3.sub.3 to exit the first prism member 3. Then, the first light
beam is led to the image pickup device 13.
[0212] In addition, the volume hologram 6 is formed by bonding
together three layers of R, G and B so that a color image can be
observed.
[0213] In all Examples 1 to 5, the image display device used
therein has a diagonal length of 0.55 inches and an aspect ratio of
4:3. The size of the image display device is 8.448 mm.times.11.264
mm in length and breadth. The central diopter is -1.0 D. Regarding
the viewing field angles, the horizontal full field angle is
30.0.degree., and the vertical full field angle is 22.7.degree..
The pupil diameter is 4 mm. The eye relief is 28.34 mm in Example
1, 27.93 mm in Example 2, 27.91 mm in Example 3, 28.34 mm in
Example 4, and 27.95 mm in Example 5.
[0214] Numerical data in each example is as follows. In the tables
below, "FFS" denotes a free-form surface, "CYL" denotes a
cylindrical surface, "HOE" denotes a reflection hologram surface,
"TOR" denotes a toric surface, and "RE" denotes a reflecting
surface.
3EXAMPLE 1 Sur- face No. Ob- Radius of Surface Refractive ject
curvature separation Displacement Abbe's No. plane .infin. -1000.00
and tilt index 1 .infin. (Pupil ) (1) 2 FFS{circle over (1)} (2)
1.5254 56.2 3 CYL{circle over (1)} (3) 1.5254 56.2 4 FFS{circle
over (2)} (RE) (4) 1.5254 56.2 5 CYL{circle over (1)} (HOE{circle
over (1)}) (3) 1.5254 56.2 6 FFS{circle over (3)} (5) Im- .infin.
(6) age plane CYL{circle over (1)} Rx -183.88 Ry .infin. FFS{circle
over (1)} C.sub.4 1.4081 .times. 10.sup.-2 C.sub.6 1.9480 .times.
10.sup.-2 C.sub.8 5.7152 .times. 10.sup.-4 C.sub.10 3.1468 .times.
10.sup.-4 C.sub.11 -9.0005 .times. 10.sup.-6 C.sub.13 -5.2999
.times. 10.sup.-5 C.sub.15 -2.0707 .times. 10.sup.-5 FFS{circle
over (2)} C.sub.4 -6.6649 .times. 10.sup.-3 C.sub.6 -3.7544 .times.
10.sup.-3 C.sub.8 1.2394 .times. 10.sup.-4 C.sub.10 2.2242 .times.
10.sup.-5 C.sub.11 -3.2898 .times. 10.sup.-6 C.sub.13 -1.4789
.times. 10.sup.-5 C.sub.15 -5.7270 .times. 10.sup.-6 FFS{circle
over (3)} C.sub.4 -5.5913 .times. 10.sup.-3 C.sub.6 -1.1475 .times.
10.sup.-2 C.sub.8 -6.6952 .times. 10.sup.-4 C.sub.10 6.7339 .times.
10.sup.-5 C.sub.11 9.2151 .times. 10.sup.-5 C.sub.13 3.7627 .times.
10.sup.-4 C.sub.15 1.5673 .times. 10.sup.-4 HOE{circle over (1)}
HV1: REA HV2: REA HOR: 1 HX1: 0.0 HY1: 0.0 HZ1: 0.0 HX2: 0.0 HY2:
0.0 HZ2: 0.0 (First Layer ) HWL: 630 H.sub.2 0.1033 .times.
10.sup.-2 H.sub.3 -0.2160 .times. 10.sup.-2 H.sub.5 -0.1062 .times.
10.sup.-2 H.sub.7 -0.1201 .times. 10.sup.-3 H.sub.9 -0.3320 .times.
10.sup.-4 H.sub.10 0.6054 .times. 10.sup.-5 H.sub.12 -0.6586
.times. 10.sup.-6 H.sub.14 -0.2407 .times. 10.sup.-6 H.sub.16
0.5397 .times. 10.sup.-6 H.sub.18 0.5652 .times. 10.sup.-8 H.sub.20
-0.1139 .times. 10.sup.-7 H.sub.21 -0.9545 .times. 10.sup.-8
H.sub.23 0.2587 .times. 10.sup.-7 H.sub.25 -0.2341 .times.
10.sup.-8 H.sub.27 0.5905 .times. 10.sup.-10 (Second Layer) HWL:
520 H2 0.7285 .times. 10.sup.-3 H.sub.3 0.1900 .times. 10.sup.-2
H.sub.5 -0.9272 .times. 10.sup.-3 H.sub.7 -0.1079 .times. 10.sup.-3
H.sub.9 -0.3038 .times. 10.sup.-4 H.sub.10 0.5751 .times. 10.sup.-5
H.sub.12 -0.1250 .times. 10.sup.-5 H.sub.14 -0.8794 .times.
10.sup.-7 H.sub.16 0.5433 .times. 10.sup.-6 H.sub.18 -0.2290
.times. 10.sup.-7 H.sub.20 0.3096 .times. 10.sup.-7 H.sub.21
-0.9701 .times. 10.sup.-8 H.sub.23 0.2835 .times. 10.sup.-7
H.sub.25 -0.2596 .times. 10.sup.-8 H.sub.27 0.1819 .times.
10.sup.-8 (Third Layer ) HWL: 470 H2 0.4134 .times. 10.sup.-3
H.sub.3 -0.1746 .times. 10.sup.-2 H.sub.5 -0.8496 .times. 10.sup.-3
H.sub.7 -0.1006 .times. 10.sup.-3 H.sub.9 -0.2702 .times. 10.sup.-4
H.sub.10 0.5553 .times. 10.sup.-5 H.sub.12 -0.1524 .times.
10.sup.-5 H.sub.14 0.7510 .times. 10.sup.-7 H.sub.16 0.5495 .times.
10.sup.-6 H.sub.18 -0.4000 .times. 10.sup.-7 H.sub.20 0.5038
.times. 10.sup.-7 H.sub.21 -0.9397 .times. 10.sup.-8 H.sub.23
0.2966 .times. 10.sup.-7 H.sub.25 -0.2949 .times. 10.sup.-8
H.sub.27 0.2580 .times. 10.sup.-8 Displacement and tilt (1) X 0.00
Y 0.00 Z 0.00 .alpha. 0.00 .beta. 0.00 .gamma. 0.00 Displacement
and tilt (2) X 0.00 Y -2.67 Z 28.34 .alpha. 10.37 .beta. 0.00
.gamma. 0.00 Displacement and tilt (3) X 0.00 Y 4.54 Z 31.74
.alpha. 20.14 .beta. 0.00 .gamma. 0.00 Displacement and tilt (4) X
0.00 Y -1.47 Z 39.62 .alpha. -12.73 .beta. 0.00 .gamma. 0.00
Displacement and tilt (5) X 0.00 Y 11.09 Z 35.79 .alpha. 69.79
.beta. 0.00 .gamma. 0.00 Displacement and tilt (6) X 0.00 Y 17.48 Z
38.23 .alpha. -116.96 .beta. 0.00 .gamma. 0.00 .theta. =
69.86.degree. Dx/Rx = -0.0613 Dx/Ry = 0 Da/Ra = -0.0944 Db/Rb = 0
Example 2 1 .infin. (Pupil ) (1) 2 FFS{circle over (1)} (2) 1.5254
56.2 3 CYL{circle over (1)} (3) 1.5254 56.2 4 FFS{circle over (2)}
(RE) (4) 1.5254 56.2 5 CYL{circle over (1)} (HOE{circle over (1)})
(3) 1.5254 56.2 6 FFS{circle over (3)} (5) Im- .infin. (6) age
plane CYL{circle over (1)} Rx .infin. Ry -167.81 FFS{circle over
(1)} C.sub.4 3.2852 .times. 10.sup.-2 C.sub.6 3.2975 .times.
10.sup.-3 C.sub.8 3.1981 .times. 10.sup.-4 C.sub.10 4.3918 .times.
10.sup.-4 C.sub.11 -1.4812 .times. 10.sup.-5 C.sub.13 -5.4025
.times. 10.sup.-5 C.sub.15 3.8057 .times. 10.sup.-5 FFS{circle over
(2)} C.sub.4 -6.4069 .times. 10.sup.-4 C.sub.6 -1.0330 .times.
10.sup.-2 C.sub.8 1.8977 .times. 10.sup.-4 C.sub.10 4.5314 .times.
10.sup.-5 C.sub.11 -7.0230 .times. 10.sup.-6 C.sub.13 -1.6251
.times. 10.sup.-5 C.sub.15 4.6406 .times. 10.sup.-6 FFS{circle over
(3)} C.sub.4 -1.5137 .times. 10.sup.-2 C.sub.6 1.6463 .times.
10.sup.-2 C.sub.8 -2.4620 .times. 10.sup.-3 C.sub.10 1.8240 .times.
10.sup.-4 C.sub.11 1.5732 .times. 10.sup.-4 C.sub.13 3.2072 .times.
10.sup.-4 C.sub.15 -2.8944 .times. 10.sup.-4 HOE{circle over (1)}
HV1: REA HV2: REA HOR: 1 HX1: 0.0 HY1: 0.0 HZ1: 0.0 HX2: 0.0 HY2:
0.0 HZ2: 0.0 (First Layer ) HWL: 630 H.sub.2 0.5585 .times.
10.sup.-2 H.sub.3 -0.2727 .times. 10.sup.-2 H.sub.5 -0.2241 .times.
10.sup.-3 H.sub.7 -0.1729 .times. H.sub.9 0.2012 .times. 10.sup.-4
H.sub.10 0.4093 .times. 10-5 10.sup.-3 H.sub.12 -0.6315 .times.
H.sub.14 0.4235 .times. 10-6 H.sub.16 0.4673 .times. 10.sup.-6
10.sup.-6 H.sub.18 0.4414 .times. 10.sup.-6 H.sub.20 -0.3938
.times. 10.sup.-6 H.sub.21 -0.1230 .times. 10.sup.-7 H.sub.23
0.3303 .times. 10.sup.-7 H25 -0.7171 .times. H.sub.27 -0.1609
.times. 10.sup.-7 10.sup.-9 (Second Layer) HWL: 520 H.sub.2 0.4590
.times. 10.sup.-2 H.sub.3 -0.2294 .times. 10.sup.-2 H.sub.5 -0.9272
.times. 10.sup.-3 H.sub.7 -0.1573 .times. 10.sup.-3 H.sub.9 0.2531
.times. 10.sup.-4 H.sub.10 0.5751 .times. 10.sup.-5 H.sub.12
-0.9114 .times. 10.sup.-6 H.sub.14 0.1040 .times. 10.sup.-5
H.sub.16 0.5433 .times. 10.sup.-6 H.sub.18 0.3726 .times. 10.sup.-6
H.sub.20 -0.3844 .times. 10.sup.-6 H.sub.21 -0.9701 .times.
10.sup.-8 H.sub.23 0.3090 .times. 10.sup.-7 H25 0.1526 .times.
10.sup.-9 H.sub.27 0.1819 .times. 10.sup.-8 (Third Layer ) HWL: 470
H.sub.2 0.3871 .times. 10.sup.-2 H.sub.3 -0.2031 .times. 10.sup.-2
H.sub.5 -0.2192 .times. 10.sup.-3 H.sub.7 -0.1416 .times. 10.sup.-3
H.sub.9 0.2737 .times. 10.sup.-4 H.sub.10 0.2333 .times. 10.sup.-5
H.sub.12 -0.5933 .times. 10.sup.-6 H.sub.14 0.1284 .times.
10.sup.-5 H.sub.16 0.4896 .times. 10.sup.-6 H.sub.18 0.3413 .times.
10.sup.-6 H.sub.20 -0.3722 .times. 10.sup.-6 H.sub.21 -0.3603
.times. 10.sup.-8 H.sub.23 0.2860 .times. 10.sup.-7 H25 -0.1499
.times. 10.sup.-8 H.sub.27 -0.1747 .times. 10.sup.-7 Displacement
and tilt (1) X 0.00 Y 0.00 Z 0.00 .alpha. 0.00 .beta. 0.00 .gamma.
0.00 Displacement and tilt (2) X 0.00 Y 0.36 Z 27.93 .alpha. 11.25
.beta. 0.00 .gamma. 0.00 Displacement and tilt (3) X 0.00 Y 3.67 Z
30.94 .alpha. 19.56 .beta. 0.00 .gamma. 0.00 Displacement and tilt
(4) X 0.00 Y -0.62 Z 38.24 .alpha. -13.13 .beta. 0.00 .gamma. 0.00
Displacement and tilt (5) X 0.00 Y 11.01 Z 34.91 .alpha. 75.07
.beta. 0.00 .gamma. 0.00 Displacement and tilt (6) X 0.00 Y 17.90 Z
36.47 .alpha. -115.50 .beta. 0.00 .gamma. 0.00 .theta. =
70.03.degree. Dx/Rx = 0 Dx/Ry = -0.0707 Da/Ra = -0.1282 Db/Rb = 0
Example 3 1 .infin. (Pupil ) (1) 2 FFS{circle over (1)} (2) 1.5254
56.2 3 .infin. (3) 1.5254 56.2 4 FFS{circle over (2)} (RE) (4)
1.5254 56.2 5 .infin. (HOE{circle over (1)}) (3) 1.5254 56.2 6
FFS{circle over (3)} (5) Im- .infin. (6) age plane FFS{circle over
(1)} C.sub.4 3.3501 .times. 10.sup.-2 C.sub.6 2.9604 .times.
10.sup.-3 C.sub.8 5.7973 .times. 10.sup.-4 C.sub.10 6.6754 .times.
10.sup.-4 C.sub.11 -9.2202 .times. 10.sup.-6 C.sub.13 -5.0913
.times. 10.sup.-5 C.sub.15 3.4518 .times. 10.sup.-5 FFS{circle over
(2)} C.sub.4 -2.5765 .times. 10.sup.-4 C.sub.6 -8.8917 .times.
10.sup.-3 C.sub.8 2.4647 .times. 10.sup.-4 C.sub.10 3.8827 .times.
10.sup.-5 C.sub.11 -6.6413 .times. 10.sup.-6 C.sub.13 -1.3699
.times. 10.sup.-5 C.sub.15 6.8648 .times. 10.sup.-6 FFS{circle over
(3)} C.sub.4 -9.5889 .times. 10.sup.-3 C.sub.6 3.3124 .times.
10.sup.-2 C.sub.8 -3.5119 .times. 10.sup.-3 C.sub.10 1.7859 .times.
10.sup.-3 C.sub.11 1.6079 .times. 10.sup.-4 C.sub.13 3.2884 .times.
10.sup.-5 C.sub.15 -3.2974 .times. 10.sup.-4 HOE{circle over (1)}
HV1: REA HV2: REA HOR: 1 HX1: 0.0 HY1: 0.0 HZ1: 0.0 HX2: 0.0 HY2:
0.0 HZ2: 0.0 (First Layer ) HW- 630 L: H2 0.5015 .times. 10.sup.-2
H.sub.3 -0.2727 .times. 10.sup.-2 H.sub.5 -0.6845 .times. 10.sup.-4
H.sub.7 -0.1253 .times. 10.sup.-3 H.sub.9 0.2997 .times. 10.sup.-4
H.sub.10 0.5917 .times. 10.sup.-5 H.sub.12 -0.9083 .times.
10.sup.-6 H.sub.14 0.1669 .times. 10.sup.-5 H.sub.16 0.3649 .times.
10.sup.-6 H.sub.18 -0.5739 .times. 10.sup.-7 H.sub.20 -0.1921
.times. 10.sup.-6 H21 -0.1067 .times. 10.sup.-7 H23 0.1352 .times.
10.sup.-7 H25 -0.1290 .times. 10.sup.-7 H.sub.27 -0.8941 .times.
10.sup.-8 (Second Layer) HW- 520 L: H2 0.4085 .times. 10.sup.-2
H.sub.3 -0.2327 .times. 10.sup.-2 H.sub.5 -0.9226 .times. 10.sup.-4
H.sub.7 -0.1099 .times. 10.sup.-3 H.sub.9 0.2933 .times. 10.sup.-4
H.sub.10 0.4942 .times. 10.sup.-5 H.sub.12 -0.8760 .times.
10.sup.-6 H.sub.14 0.1990 .times. 10.sup.-5 H.sub.16 0.4349 .times.
10.sup.-6 H.sub.18 -0.9260 .times. 10.sup.-7 H.sub.20 -0.1725
.times. 10.sup.-6 H21 -0.5201 .times. 10.sup.-8 H23 0.1461 .times.
10.sup.-7 H25 -0.1144 .times. 10.sup.-7 H.sub.27 -0.1007 .times.
10.sup.-7 (Third Layer ) HW- 470 L: H2 0.3396 .times. 10.sup.-2
H.sub.3 -0.2090 .times. 10.sup.-2 H.sub.5 -0.1106 .times. 10.sup.-3
H.sub.7 -0.9409 .times. 10.sup.-4 H.sub.9 0.2936 .times. 10.sup.-4
H.sub.10 0.4540 .times. 10.sup.-5 H.sub.12 -0.4906 .times.
10.sup.-6 H.sub.14 0.2100 .times. 10.sup.-5 H.sub.16 0.4005 .times.
10.sup.-6 H.sub.18 -0.1097 .times. 10.sup.-6 H.sub.20 -0.1643
.times. 10.sup.-6 H21 -0.4518 .times. 10.sup.-8 H23 0.1283 .times.
10.sup.-7 H25 -0.1245 .times. 10.sup.-7 H.sub.27 -0.9771 .times.
10.sup.-8 Displacement and tilt (1) X 0.00 Y 0.00 Z 0.00 .alpha.
0.00 .beta. 0.00 .gamma. 0.00 Displacement and tilt (2) X 0.00 Y
0.37 Z 27.91 .alpha. 13.67 .beta. 0.00 .gamma. 0.00 Displacement
and tilt (3) X 0.00 Y 2.73 Z 30.67 .alpha. 16.01 .beta. 0.00
.gamma. 0.00 Displacement and tilt (4) X 0.00 Y 0.09 Z 37.63
.alpha. -13.84 .beta. 0.00 .gamma. 0.00 Displacement and tilt (5) X
0.00 Y 10.95 Z 35.87 .alpha. 80.36 .beta. 0.00 .gamma. 0.00
Displacement and tilt (6) X 0.00 Y 18.32 Z 36.73 .alpha. -119.42
.beta. 0.00 .gamma. 0.00 .theta. = 73.99.degree. Dx/Rx = 0 Dx/Ry =
0 Da/Ra = 0 Db/Rb = 0 Example 4 1 .infin. (Pupil ) (1) 2 FFS{circle
over (1)} (2) 1.5254 56.2 3 TOR{circle over (1)} (3) 1.5254 56.2 4
FFS{circle over (2)} (RE) (4) 1.5254 56.2 5 TOR{circle over (1)}
(HOE{circle over (1)}) (3) 1.5254 56.2 6 FFS{circle over (3)} (5)
Im- .infin. (6) age plane TOR{circle over (1)} Rx -186.67 Ry
-1921.54 FFS{circle over (1)} C.sub.4 1.4572 .times. 10.sup.-2
C.sub.6 1.9424 .times. 10.sup.-2 C.sub.8 5.6118 .times. 10.sup.-4
C.sub.10 3.0191 .times. 10.sup.-4 C.sub.11 -5.5671 .times.
10.sup.-6 C.sub.13 -5.7474 .times. 10.sup.-5 C.sub.15 -2.0993
.times. 10.sup.-5 FFS{circle over (2)} C.sub.4 -6.5615 .times.
10.sup.-3 C.sub.6 -3.9808 .times. 10.sup.-3 C.sub.8 1.1615 .times.
10.sup.-4 C.sub.10 2.5034 .times. 10.sup.-5 C.sub.11 -2.4825
.times. 10.sup.-6 C.sub.13 -1.5860 .times. 10.sup.-5 C.sub.15
-5.8682 .times. 10.sup.-6 FFS{circle over (3)} C.sub.4 -5.3015
.times. 10.sup.-3 C.sub.6 -1.2565 .times. 10.sup.-2 C.sub.8 -6.6936
.times. 10.sup.-4 C.sub.10 1.0147 .times. 10.sup.-5 C.sub.11 8.2407
.times. 10.sup.-5 C.sub.13 3.9328 .times. 10.sup.-4 C.sub.15 1.7057
.times. 10.sup.-4 HOE{circle over (1)} HV1: REA HV2: REA HOR: 1
HX1: 0.0 HY1: 0.0 HZ1: 0.0 HX2: 0.0 HY2: 0.0 HZ2: 0.0 (First Layer
) HW- 630 L: H2 0.1210 .times. 10.sup.-2 H.sub.3 -0.2183 .times.
H.sub.5 -0.1060 .times. 10-2 10.sup.-2 H.sub.7 -0.1201 .times.
10.sup.-3 H.sub.9 -0.3374 .times. H.sub.10 0.5781 .times. 10-5
10.sup.-4 H.sub.12 -0.5260 .times. 10.sup.-6 H.sub.14 -0.2197
.times. 10.sup.-6 H.sub.16 0.5362 .times. 10-6 H.sub.18 0.1622
.times. 10.sup.-7 H.sub.20 -0.1139 .times. 10.sup.-7 H21 -0.8656
.times. 10.sup.-8 H23 0.2598 .times. 10.sup.-7 H25 -0.2152 .times.
H.sub.27 0.1856 .times. 10-10 10.sup.-8 (Second Layer) HW- 520 L:
H2 0.8868 .times. 10.sup.-3 H.sub.3 -0.1923 .times. 10.sup.-2
H.sub.5 -0.9251 .times. 10.sup.-3 H.sub.7 -0.1079 .times. 10.sup.-3
H.sub.9 -0.3086 .times. 10.sup.-4 H.sub.10 0.5549 .times. 10.sup.-5
H.sub.12 -0.1148 .times. 10.sup.-5 H.sub.14 -0.7706 .times.
10.sup.-7 H.sub.16 0.5434 .times. 10.sup.-6 H.sub.18 -0.1750
.times. 10.sup.-7 H.sub.20 0.3104 .times. 10.sup.-7 H21 -0.8797
.times. 10.sup.-8 H23 0.2840 .times. 10.sup.-7 H25 -0.2596 .times.
10.sup.-8 H.sub.27 0.1818 .times. 10.sup.-8 (Third Layer ) HW- 470
L: H2 0.5610 .times. 10.sup.-3 H.sub.3 -0.1773 .times. 10.sup.-2
H.sub.5 -0.8460 .times. 10.sup.-3 H.sub.7 -0.1003 .times. 10.sup.-3
H.sub.9 -0.2778 .times. 10.sup.-4 H.sub.10 0.5545 .times. 10.sup.-5
H.sub.12 -0.1523 .times. 10.sup.-5 H.sub.14 0.7890 .times.
10.sup.-7 H.sub.16 0.5497 .times. 10.sup.-6 H.sub.18 -0.3994
.times. 10.sup.-7 H.sub.20 0.5314 .times. 10.sup.-7 H21 -0.9383
.times. 10.sup.-8 H23 0.2987 .times. 10.sup.-7 H25 -0.2959 .times.
10.sup.-8 H.sub.27 0.2687 .times. 10.sup.-8 Displacement and tilt
(1) X 0.00 Y 0.00 Z 0.00 .alpha. 0.00 .beta. 0.00 .gamma. 0.00
Displacement and tilt (2) X 0.00 Y -2.59 Z 28.33 .alpha. 10.27
.beta. 0.00 .gamma. 0.00 Displacement and tilt (3) X 0.00 Y 4.53 Z
31.72 .alpha. 20.19 .beta. 0.00 .gamma. 0.00 Displacement and tilt
(4) X 0.00 Y -1.38 Z 39.58 .alpha. -12.78 .beta. 0.00 .gamma. 0.00
Displacement and tilt (5) X 0.00 Y 11.08 Z 35.82 .alpha. 69.78
.beta. 0.00 .gamma. 0.00 Displacement and tilt (6) X 0.00 Y 17.48 Z
38.14 .alpha. -116.76 .beta. 0.00 .gamma. 0.00 .theta. =
69.83.degree. Dx/Rx = -0.0603 Dx/Ry -0.0059 Da/Ra = -0.0928 Db/Rb =
-0.0112 Example 5 1 .infin. (Pupil ) (1) 2 FFS{circle over (1)} (2)
1.5254 56.2 3 -2000 (3) 1.5254 56.2 4 FFS{circle over (2)} (RE) (4)
1.5254 56.2 5 -2000 (HOE{circle over (1)}) (3) 1.5254 56.2 6
FFS{circle over (3)} (5) Im- .infin. (6) age plane FFS{circle over
(1)} C.sub.4 3.2480 .times. 10.sup.-2 C.sub.6 2.9376 .times.
10.sup.-3 C.sub.8 6.3684 .times. 10.sup.-4 C.sub.10 6.6437 .times.
10.sup.-4 C.sub.11 -1.1018 .times. 10.sup.-5 C.sub.13 -4.7966
.times. 10.sup.-5 C.sub.15 3.1555 .times. 10.sup.-5 FFS{circle over
(2)} C.sub.4 -6.3947 .times. 10.sup.-4 C.sub.6 -8.9236 .times.
10.sup.-3 C.sub.8 2.5164 .times. 10.sup.-4 C.sub.10 5.4004 .times.
10.sup.-5 C.sub.11 -7.1084 .times. 10.sup.-6 C.sub.13 -1.3112
.times. 10.sup.-5 C.sub.15 6.0361 .times. 10.sup.-6 FFS{circle over
(3)} C.sub.4 -9.3660 .times. 10.sup.-3 C.sub.6 3.1207 .times.
10.sup.-2 C.sub.8 -3.4094 .times. 10.sup.-3 C.sub.10 1.6934 .times.
10.sup.-3 C.sub.11 1.5776 .times. 10.sup.-4 C.sub.13 7.0544 .times.
10.sup.-5 C.sub.15 -3.2674 .times. 10.sup.-4 HOE{circle over (1)}
HV1: REA HV2: REA HOR: 1 HX1: 0.0 HY1: 0.0 HZ1: 0.0 HX2: 0.0 HY2:
0.0 HZ2: 0.0 (First Layer ) HW- 630 L: H2 5.8162 .times. 10.sup.-3
H.sub.3 -2.7701 .times. 10.sup.-3 H.sub.5 -7.1217 .times. 10.sup.-5
H.sub.7 -1.7079 .times. 10.sup.-4 H.sub.9 1.8808 .times. 10.sup.-5
H.sub.10 6.2670 .times. 10.sup.-6 H.sub.12 -2.8904 .times.
10.sup.-6 H.sub.14 1.2124 .times. 10.sup.-6 H.sub.16 7.0035 .times.
10.sup.-7 H.sub.18 4.4748 .times. 10.sup.-8 H.sub.20 -1.5532
.times. 10.sup.-7 H21 -6.1624 .times. 10.sup.-9 H23 2.9660 .times.
10.sup.-8 H25 -7.0306 .times. 10.sup.-9 H.sub.27 -7.1544 .times.
10.sup.-9 (Second
Layer) HW- 520 L: H2 4.8663 .times. 10.sup.-3 H.sub.3 -2.3849
.times. 10.sup.-3 H.sub.5 -9.0966 .times. 10.sup.-5 H.sub.7 -1.5366
.times. 10.sup.-4 H.sub.9 1.8804 .times. 10.sup.-5 H.sub.10 5.3088
.times. 10.sup.-6 H.sub.12 -2.7147 .times. 10.sup.-6 H.sub.14
1.4933 .times. 10.sup.-6 H.sub.16 7.4193 .times. 10.sup.-7 H.sub.18
5.0327 .times. 10.sup.-9 H.sub.20 -1.3634 .times. 10.sup.-7 H21
-1.0116 .times. 10.sup.-9 H23 2.8504 .times. 10.sup.-8 H25 -5.8172
.times. 10.sup.-9 H.sub.27 7.9636 .times. 10.sup.-9 (Third Layer )
HW- 470 L: H2 4.1797 .times. 10.sup.-3 H.sub.3 -2.1530 .times.
10.sup.-3 H.sub.5 -1.0820 .times. 10.sup.-4 H.sub.7 -1.3803 .times.
10.sup.-4 H.sub.9 1.8955 .times. 10.sup.-5 H.sub.10 4.8880 .times.
10.sup.-6 H.sub.12 -2.3165 .times. 10.sup.-6 H.sub.14 1.5907
.times. 10.sup.-6 H.sub.16 7.1219 .times. 10.sup.-7 H.sub.18
-1.3661 .times. 10.sup.-8 H.sub.20 -1.2815 .times. 10.sup.-7 H21
-2.4660 .times. 10.sup.-10 H23 2.7210 .times. 10.sup.-8 H25 -7.2245
.times. 10.sup.-9 H.sub.27 -7.5296 .times. 10.sup.-9 Displacement
and tilt (1) X 0.00 Y 0.00 Z 0.00 .alpha. 0.00 .beta. 0.00 .gamma.
0.00 Displacement and tilt (2) X 0.00 Y 0.00 Z 0.00 .alpha. 0.00
.beta. 0.00 .gamma. 0.00 Displacement and tilt (3) X 0.00 Y 2.75 Z
30.72 .alpha. 16.00 .beta. 0.00 .gamma. 0.00 Displacement and tilt
(4) X 0.00 Y 0.11 Z 37.68 .alpha. -13.85 .beta. 0.00 .gamma. 0.00
Displacement and tilt (5) X 0.00 Y 10.97 Z 35.93 .alpha. 79.77
.beta. 0.00 .gamma. 0.00 Displacement and tilt (6) X 0.00 Y 18.33 Z
36.75 .alpha. -119.27 .beta. 0.00 .gamma. 0.00 .theta. =
73.92.degree. Dx/Rx = -0.0094 Dx/Ry = -0.0094 Da/Ra = -0.0111 Db/Rb
= -0.0087
[0215] Image distortion in Example 1 is shown in FIG. 6, and
lateral aberrations in the wavelength regions R, G and B in Example
1 are shown in FIGS. 7 to 9, representatively. In the diagrams
showing lateral aberrations, the numerals in the parentheses denote
(horizontal field angle, vertical field angle), and lateral
aberrations at the field angles are shown.
[0216] FIG. 11 is a sectional view of a viewing optical system as
in the foregoing examples, taken along a YZ-plane containing an
optical axis thereof, which shows that light passing through the
volume hologram 6 without being diffracted may give an adverse
effect as ghost light.
[0217] Even when a light beam is incident on the volume hologram 6
at the first incident angle in the optical system arranged as in
the foregoing examples, light rays in a predetermined wavelength
region are not 100% diffracted and reflected, but there may be a
slight amount of unwanted order of light that is not diffracted and
reflected but passes through the volume hologram 6, as shown in
FIG. 11 by way of example.
[0218] The undesirably transmitted light may impinge on the bottom
surface 4.sub.3 or side surface (surface extending in a direction
perpendicular to the plane of the figure) of the ocular optical
system as shown in FIG. 11, by way of example, and the reflected
light from the bottom surface 4.sub.3 or the like may enter the
observer's eyeball as ghost light.
[0219] In the present invention, as shown in FIG. 10, the side
surfaces of the first prism member 3 and the side surface and
bottom surface 4.sub.3 of the second prism member 4 are each
painted with a member having the property of absorbing light, e.g.
black paint, as a ghost light eliminating member in addition to the
arrangement as shown in each of FIGS. 1 to 5. It should be noted
that ghost light eliminating members 15 should preferably be
provided on regions included in non-optical functional surfaces
(i.e. surfaces other than the optical functional surfaces of the
first and second prism members 3 and 4 that transmit or reflect the
first light beam), such as the region outside the ray effective
diameter of the first entrance surface 3.sub.1 of the first prism
member 3, the region outside the ray effective diameter of the
reflecting surface 3.sub.2 of the first prism member 3, and the
region outside the ray effective diameter of the second exit
surface 4.sub.1 of the second prism member 4.
[0220] The above-described viewing optical system and image pickup
optical system according to the present invention can be used as
viewing apparatus in which an object image is viewed through an
ocular lens, or as photographic apparatus in which an object image
is formed and the formed image is received with an image pickup
device, such as a CCD or a silver halide film, to take a photograph
of the object. Specific examples of such apparatus are microscopes,
head-mounted image display apparatus, endoscopes, projectors,
silver halide cameras, digital cameras, VTR cameras, and
information processing apparatus incorporating a photographic
apparatus, such as personal computers and portable telephones.
Embodiments in which the present invention is applied to such
apparatuses will be described below.
[0221] As one example, a head-mounted image display apparatus
arranged for two eyes is shown in FIG. 12. The figure shows the
image display apparatus in a state where it is fitted on an
observer's head. FIG. 13 is a sectional view of the image display
apparatus. As shown in FIG. 13, a viewing optical system according
to the present invention is used as an ocular optical system 100
having an image display device 5. A pair of ocular optical systems
100 are prepared for the left and right eyes and supported apart
from each other by the interpupillary distance, i.e. the distance
between the two eyes, thereby forming a stationary or portable
image display apparatus 102, such as a head-mounted image display
apparatus, which enables the observer to see with both eyes.
[0222] More specifically, the display apparatus body unit 102 is
equipped with a pair of ocular optical systems 100 (left and right)
. The above-described viewing optical system is used as each ocular
optical system 100. Image display devices 5, which are liquid
crystal display devices, are disposed in the respective image
planes of the two ocular optical systems 100. As shown in FIG. 12,
the display apparatus body unit 102 is provided with temporal
frames 103 that are contiguous with the left and right ends thereof
so that the display apparatus body unit 102 can be held in front of
the observer's eyes. As shown in FIG. 13, a cover member 91 is
placed between the exit pupil of the ocular optical system 100 and
the second exit surface 4.sub.1 of the second prism member 4. As
the cover member 91, any of a plane-parallel plate, a positive lens
and a negative lens can be used.
[0223] Further, a speaker 104 is provided on each temporal frame
103 to enable the user to enjoy listening to stereophonic sound in
addition to image observation. The display apparatus body unit 102
having the speakers 104 is connected with a replaying unit 106,
e.g. a portable video cassette unit, through an image and sound
transmitting cord 105. Therefore, the user can enjoy not only
observing an image but also listening to sound with the replaying
unit 106 retained on a desired position, e.g. a belt, as
illustrated in FIG. 12. Reference numeral 107 in FIG. 12 denotes a
switch and volume control part of the replaying unit 106. It should
be noted that the display apparatus body unit 102 contains
electronic parts such as image and sound processing circuits.
[0224] The cord 105 may have a jack and plug arrangement attached
to the distal end thereof so that the cord 105 can be detachably
connected to an existing video deck. The cord 105 may also be
connected to a TV signal receiving tuner so as to enable the user
to enjoy watching TV. Alternatively, the cord 105 may be connected
to a computer to receive computer graphic images or message images
or the like from the computer. To eliminate the bothersome cord,
the image display apparatus may be arranged to receive external
radio signals through an antenna connected thereto.
[0225] The viewing optical system according to the present
invention may also be used in a head-mounted image display
apparatus for a single eye by placing the ocular optical system in
front of either of the left and right eyes. FIG. 14 shows the
head-mounted image display apparatus for a single eye in a state
where it is fitted on an observer's head (in this case, the
apparatus is fitted for the left eye). In the illustrated
arrangement, a display apparatus body unit 102 having one set of
ocular optical system 100 with an image display device 5 is mounted
on a front frame 108 so as to lie in front of the associated eye of
the observer. As shown in FIG. 14, the front frame 108 is provided
with temporal frames 103 that are contiguous with the left and
right ends thereof so that the display apparatus body unit 102 can
be held in front of one eye of the observer. The arrangement of the
rest of the apparatus is the same as in the case of FIG. 12.
Therefore, a description thereof is omitted.
[0226] FIGS. 15 to 17 are conceptual views showing an arrangement
in which an image pickup optical system according to the present
invention is incorporated into an objective optical system
constituting a finder unit of an electronic camera 40. FIG. 15 is a
perspective view showing the external appearance of the electronic
camera 40 as viewed from the front side thereof. FIG. 16 is a
perspective view of the electronic camera 40 as viewed from the
rear side thereof. FIG. 17 is a sectional view showing the
arrangement of the electronic camera 40.
[0227] In the illustrated example, the electronic camera 40
includes a photographic optical system 41 having an optical path 42
for photography, a finder optical system 43 having an optical path
44 for the finder, a shutter button 45, a flash 46, a liquid
crystal display monitor 47, etc. When the shutter button 45, which
is placed on the top of the camera 40, is depressed, photography is
performed through an objective optical system 48 for photography.
An object image produced by the objective optical system 48 for
photography is formed on an image pickup surface 50 of a CCD 49
through a filter 51, e.g. a low-pass filter, an infrared cutoff
filter, etc.
[0228] The object image received by the CCD 49 is processed in a
processor 52 and displayed as an electronic image on the liquid
crystal display monitor 47, which is provided on the rear of the
camera 40. A recording device 61 is connected to the processor 52
to enable the photographed electronic image to be recorded. It
should be noted that the recording device 61 may be provided
separately from the processor 52. The arrangement may also be such
that the photographed electronic image is electronically recorded
or written on a floppy disk or the like. The camera 40 may be
arranged in the form of a silver halide camera in which a silver
halide film is disposed in place of the CCD 49.
[0229] Furthermore, an objective optical system 53 for the finder
is placed in the optical path 44 for the finder. The objective
optical system 53 for the finder comprises a cover lens 54, a
positive lens unit 57 movable in the optical axis direction for
focusing, an aperture stop 14, a first prism member 3 and a second
prism member 4. The cover lens 54 used as a cover member is a lens
unit having a negative power to enlarge the field angle. It should
be noted that the first prism member 3 has a reflecting surface 34
in an optical path along which diffracted and reflected light from
a hologram 6 provided on the fourth entrance surface 31 travels to
reach the fourth exit surface 3.sub.3, in addition to the
arrangement of the first prism member 3 in Examples 1 to 5 of the
present invention. An object image produced on an image-formation
plane 90 by the objective optical system 53 for the finder is
formed on a view frame of a Porro prism 55, which is an
image-erecting member.
[0230] It should be noted that the view frame is placed between a
first reflecting surface 56.sub.1 and a second reflecting surface
562 of the Porro prism 55. The Porro prism 55 has the first to
fourth reflecting surfaces 56.sub.1 to 56.sub.4. An ocular optical
system 59 is placed behind the Porro prism 55 to lead an erect
image to an observer's eyeball E.
[0231] In the camera 40, which is arranged as stated above, the
objective optical system 53 for the finder can be constructed with
a minimal number of optical members. Accordingly, a
high-performance and low-cost camera can be realized. In addition,
because the optical path of the objective optical system 53 can be
folded, the degree of freedom with which the constituent elements
can be arranged in the camera increases. This is favorable for
design.
[0232] Although no mention is made of the arrangement of the
objective optical system 48 for photography in the electronic
camera 40 shown in FIG. 17, it should be noted that the objective
optical system 48 for photography may be formed by using not only a
refracting coaxial optical system but also any type of image pickup
optical systems according to the present invention, which comprise
two prism members 3 and 4, as shown in Examples 1 to 5 of the
present invention.
[0233] The ocular optical system 59 may be arranged by using any
type of ocular optical members according to the present invention,
which comprises two prism members 3 and 4, as shown in Examples 1
to 5 of the present invention.
[0234] FIG. 18 is a conceptual view showing an arrangement in which
an image pickup optical system according to the present invention
is incorporated into an objective optical system 48 in a
photography part of an electronic camera 40 and a viewing optical
system according to the present invention is incorporated in an
ocular optical system 59 of the electronic camera 40. In this
example, objective optical system 48 for photography, which is
placed in an optical path 42 for photography, includes a cover
member 62 formed from a positive lens and any type of image pickup
optical systems according to the present invention, which comprises
two prism members 3 and 4, as shown in Examples 1 to 5 of the
present invention. In addition, a filter 51, e.g. a low-pass
filter, an infrared cutoff filter, etc., is placed between the
first prism member 3 and a CCD 49. An object image produced by the
objective optical system 48 for photography is formed on an image
pickup surface 50 of the CCD 49. The object image received by the
CCD 49 is processed in a processor 52 and displayed in the form of
an electronic image on a liquid crystal display device (LCD) 60.
The processor 52 also controls a recording device 61 for recording
the object image detected by the CCD 49 in the form of electronic
information. The image displayed on the LCD 60 is led to an
observer's eyeball E through an ocular optical system 59.
[0235] The ocular optical system 59 comprises decentered prism
optical systems 3 and 4 having a similar form to that of the
viewing optical system as shown in Examples 1 and 2 of the present
invention, and a cover lens 91 disposed on the exit pupil side of
the decentered prism optical systems 3 and 4. In addition, a
backlight 92 is disposed behind the LCD 60 to illuminate it. It
should be noted that the objective optical system 48 for
photography may include another lens (positive or negative lens) as
a constituent element on the object or image side of the two prism
members 3 and 4.
[0236] In the camera 40 arranged as stated above, the objective
optical system 48 for photography and the ocular optical system 59
can be constructed with a minimal number of optical members.
Accordingly, a high-performance and low-cost camera can be
realized. In addition, because all the constituent elements of the
optical system can be arranged in the same plane, it is possible to
reduce the thickness in a direction perpendicular to the plane in
which the constituent elements are arranged.
[0237] Although in this example a positive lens is placed as a
cover member 65 of the objective optical system 48 for photography,
it is also possible to use a negative lens or a plane-parallel
plate as the cover member 65.
[0238] The surface closest to the object side in the image pickup
optical system according to the present invention may be used as a
cover member instead of providing a cover member separately. In
this example, the third entrance surface 4.sub.1 of the second
prism member 4 is the closest to the object side in the image
pickup optical system. In such a case, however, because the
entrance surface 4.sub.1 is decentered with respect to the optical
axis, if this surface is placed on the front side of the camera, it
gives the illusion that the photographic center of the camera 40 is
deviated from the subject when the entrance surface is seen from
the subject side (the subject normally feels that photographing is
being performed in a direction perpendicular to the entrance
surface, as in the case of ordinary cameras). Thus, the entrance
surface would give a sense of incongruity. Therefore, in a case
where the surface of the image-forming optical system that is
closest to the object side is a decentered surface as in this
example, it is desirable to provide the cover member 65 (or cover
lens 54) from the viewpoint of preventing the subject from feeling
incongruous when seeing the entrance surface, and allowing the
subject to be photographed with the same feeling as in the case of
the existing cameras.
[0239] FIGS. 19(a) and 19(b) are conceptual views showing an
arrangement in which an image pickup optical system according to
the present invention is incorporated into an objective optical
system 82 in an observation system of a video endoscope system, and
a viewing optical system according to the present invention is also
incorporated into an ocular optical system 87 in the observation
system of the video endoscope system. In this example, the
objective optical system 82 and the ocular optical system 87 in the
observation system each use an optical system approximately similar
in configuration to Examples 1 to 5. As shown in FIG. 19(a), the
video endoscope system includes a video endoscope 71, a light
source unit 72 for supplying illuminating light, a video processor
73 for executing processing of signals associated with the video
endoscope 71, a monitor 74 for displaying video signals output from
the video processor 73, a VTR deck 75 and a video disk 76, which
are connected to the video processor 73 to record video signals and
so forth, and a video printer 77 for printing out video signals in
the form of images. The video endoscope system further includes a
head-mounted image display apparatus (HMD) 78 such as that shown in
FIG. 12 by way of example. The video endoscope 71 has an insert
part 79 with a distal end portion 80 and an eyepiece part 81. The
distal end portion 80 and the eyepiece part 81 are arranged as
shown in FIG. 19(b).
[0240] A light beam from the light source unit 72 passes through a
light guide fiber bundle 88 and illuminates a part to be observed
through an objective optical system 89 for illumination. Light from
the part to be observed enters the objective optical system 82 for
observation through a cover member 85. Thus, an object image is
formed by the objective optical system 82. The object image is
formed on the image pickup surface of a CCD 84 through a filter 83,
e.g. a low-pass filter, an infrared cutoff filter, etc.
Furthermore, the object image is converted into a video signal by
the CCD 84. The video signal is displayed directly on the monitor
74 by the video processor 73, which is shown in FIG. 19(a). In
addition, the video signal is recorded in the VTR deck 75 and on
the video disk 76 and also printed out in the form of an image from
the video printer 77. In addition, the object image is displayed on
the image display device 5 (see FIG. 13) of the HMD 78, thereby
allowing a person wearing the HMD 78 to observe the displayed
image. At the same time, the video signal converted by the CCD 84
is displayed in the form of an electronic image on a liquid crystal
display device (LCD) 86 in the eyepiece part 81 through a video
signal transmitting device 93. The displayed image is led to an
observer's eyeball E through the ocular optical system 87, which is
formed from a viewing optical system according to the present
invention.
[0241] The endoscope arranged as stated above can be constructed
with a minimal number of optical members. Accordingly, a
high-performance and low-cost endoscope can be realized. Moreover,
because the constituent elements of the objective optical system 82
are arranged in series in the direction of the longitudinal axis of
the endoscope, the above-described advantageous effects can be
obtained without hindering the achievement of a reduction in the
diameter of the endoscope.
[0242] FIGS. 20 to 22 are conceptual views showing an arrangement
in which an image pickup optical system according to the present
invention is incorporated in a personal computer as an example of
information processing apparatus.
[0243] FIG. 20 is a perspective view of a personal computer 300 as
seen from the front side thereof in a state where a cover thereof
is open. FIG. 21 is a sectional view of a photographic optical
system 303 of the personal computer 300, and FIG. 22 is a side view
of the personal computer 300 shown in FIG. 20. As shown in FIGS. 20
to 22, the personal computer 300 has a keyboard 301 used by an
operator to input information externally, and information
processing and recording devices (not shown). The personal computer
300 further has a monitor 302 for displaying information for the
operator, and a photographic optical system 303 for taking a
photograph of the operator or an image of a surrounding object. In
this case, the monitor 302 may be a transmissive liquid crystal
display, which is illuminated from the rear side by a backlight
(not shown), or a reflective liquid crystal display, which displays
information by reflecting light applied from the front side
thereof. The monitor 302 may also be a CRT display or the like.
Although the photographic optical system 303 is incorporated in a
portion at the top right corner of the monitor 302, the position of
the photographic optical system 303 is not necessarily limited to
the illustrated position. The photographic optical system 303 may
be provided at any position around the monitor 302 or around the
keyboard 301.
[0244] The photographic optical system 303 has, in a photographic
optical path 304, an objective optical system 200 comprising an
image pickup optical system according to the present invention, and
an image pickup chip 204 for receiving an image. These constituent
elements are incorporated in the personal computer 300.
[0245] In this case, the image pickup chip 204 has additionally an
IR cutoff filter 203 integrally stuck thereon to form an image
pickup unit 206. Thus, the image pickup unit 206 can be mounted in
a one-touch simple operation by fitting it to the rear end of a
lens frame 201 of the objective optical system 200. Accordingly, it
is unnecessary to perform centering of the objective optical system
200 and the image pickup chip 204 and adjustment of surface
separation. Therefore, the assembly is easy. A cover glass 202 is
disposed at the distal end of the lens frame 201 to protect the
objective optical system 200.
[0246] An object image received by the image pickup chip 204 is
input to a processing device of the personal computer 300 through
terminals 205 and displayed on the monitor 302 in the form of an
electronic image. FIG. 20 shows a photographed image 305 of the
operator as an example of the electronic image. The image 305 can
also be transferred so as to be displayed on a personal computer of
the person on the other end of a communication line from a remote
place through the processing device via the internet or telephone
lines.
[0247] FIGS. 23(a) to 23(c) show a telephone as another example of
information processing apparatus, particularly an example in which
an image pickup optical system according to the present invention
is incorporated in a portable telephone, which is handy to
carry.
[0248] FIG. 23(a) is a front view of a portable telephone 400, and
FIG. 23(b) is a side view thereof. FIG. 23(c) is a sectional view
of a photographic optical system 405. As shown in FIGS. 23(a) to
23(c), the portable telephone 400 has a microphone unit 401 for
inputting the voice of the operator as information and a speaker
unit 402 for outputting the voice of the person on the other end of
a communication line. The portable telephone 400 further has input
keys 403 used by the operator to input information, and a monitor
404 for displaying information, e.g. a photographed image of the
operator or the person on the other end of the line and a telephone
number. In addition, the portable telephone 400 has a photographic
optical system 405, an antenna 406 for transmitting and receiving
electric waves for telephonic communication, and a processing unit
(not shown) for processing image information, communication
information, input signals, etc. The monitor 404 is a liquid
crystal display device. The layout of the constituent elements
shown in the figures is not necessarily limited to the illustrated
layout. The photographic optical system 405 has an objective
optical system 200 comprising an image pickup optical system
according to the present invention, and an image pickup chip 204
for receiving an image. The objective optical system 200 and the
image pickup chip 204 are placed in a photographic optical path 407
and incorporated in the portable telephone 400.
[0249] In this case, the image pickup chip 204 has additionally an
IR cutoff filter 203 integrally stuck thereon to form an image
pickup unit 206. Thus, the image pickup unit 206 can be mounted in
a one-touch simple operation by fitting it to the rear end of, a
lens frame 201 of the objective optical system 200. Accordingly, it
is unnecessary to perform centering of the objective optical system
200 and the image pickup chip 204 and adjustment of surface
separation. Therefore, the assembly is easy. A cover glass 202 is
disposed at the distal end of the lens frame 201 to protect the
objective optical system 200.
[0250] An object image received by the image pickup chip 204 is
input to the processing unit (not shown) through terminals 205 and
displayed in the form of an electronic image on the monitor 404 or
on the monitor of a person on the other end of a communication
line. Alternatively, the object image is displayed on both the
monitors. The processing unit further includes a signal processing
function to covert information concerning the object image received
by the image pickup chip 204 into a transmittable signal when the
image is to be transmitted to the person on the other end of the
communication line.
[0251] FIG. 28 shows a desirable arrangement for the optical system
according to the present invention when a diffractive element such
as a volume hologram is provided in a prism constituting the
optical system. In the figure, decentered prism members P1 and P2
are a first prism member 3 and a second prism member 4 included in
the viewing optical system or the image pickup optical system
according to the present invention. When the image plane C (e.g.
the display surface of the image display device 5 or the image
pickup surface of the image pickup device 13) forms a quadrangle as
shown in the figure, it is desirable from the viewpoint of forming
a beautiful image to place the decentered prism members P1 and P2
so that when the first-first surface (the first entrance surface 33
of the first prism member 3) of the decentered prism member P1 or
the second-second surface (the second exit surface 4.sub.1 of the
second prism member 4) of the decentered prism member P2 is formed
in the shape of a plane-symmetry free-form surface, the plane D of
symmetry of the plane-symmetry free-form surface is parallel to at
least one of the four sides forming the image plane C.
[0252] When the image plane C has a shape in which each of the four
interior angles is approximately 90 degrees, such as a square or a
rectangle, it is desirable that the plane D of symmetry of the
plane-symmetry free-form surface should be parallel to two sides of
the image plane C that are parallel to each other. It is more
desirable that the plane D of symmetry should lie at the middle
between the two parallel sides and coincide with a position where
the image plane C is in a symmetry between the right and left
halves or between the upper and lower halves. The described
arrangement enables the required assembly accuracy to be readily
obtained when the optical system is incorporated into an apparatus,
and is useful for mass-production.
[0253] When a plurality or all of the optical surfaces constituting
the decentered prism members P1 and P2, i.e. the first-first
surface (the first entrance surface 3.sub.3 of the first prism
member 3), the first-second surface (the first exit surface 3.sub.1
of the first prism member 3), the first-third surface (the
reflecting surface 3.sub.2 of the first prism member 3), the
second-first surface (the second entrance surface 4.sub.2 of the
second prism member 4), and the second-second surface (the second
exit surface 4.sub.1 of the second prism member 4), are
plane-symmetry free-form surfaces, it is desirable from the
viewpoint of design and aberration correcting performance to
arrange the decentered prism members P1 and P2 so that the planes
of symmetry of the plurality or all of the optical surfaces are in
the same plane D. In addition, it is desirable that the plane D of
symmetry and the plane of symmetry in power of the diffractive
element 6 should be in the above-described relationship.
[0254] In the foregoing, the viewing optical system and the image
pickup optical system according to the present invention, together
with the apparatus using either or both of the optical systems,
have been described on the basis of the embodiments thereof. It
should be noted, however, that the present invention is not
necessarily limited to the foregoing embodiments but can be
modified in a variety of ways.
[0255] Thus, it is possible according to the present invention to
provide a viewing optical system that allows observation of a
bright displayed image favorably corrected for aberrations and also
provide an image pickup optical system capable of picking up a
bright object image favorably corrected for aberrations. The
viewing optical system and the image pickup optical system are easy
to assemble, resistant to impact such as vibration, lightweight and
compact. The present invention also provides apparatus using the
viewing optical system and/or the image pickup optical system.
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